Algebra 2 Cheat Sheet
1. Basic Concepts
1.1 Complex Numbers
Complex numbers are numbers that have a real part and an imaginary part. The standard form is \(a + bi\), where \(a\) is the real part and \(bi\) is the imaginary part.
Operations:
- Addition/Subtraction: Combine like terms (real parts with real parts, imaginary parts with imaginary parts).
- Multiplication: Use the distributive property and remember that \(i^2 = -1\).
- Division: Multiply the numerator and denominator by the conjugate of the denominator and simplify.
Example 1:
Add the complex numbers \( (3 + 2i) \) and \( (1 - 4i) \).
- Combine the real parts: \( 3 + 1 = 4 \)
- Combine the imaginary parts: \( 2i - 4i = -2i \)
- Result: \( 4 - 2i \)
Example 2:
Multiply the complex numbers \( (2 + 3i)(1 - 2i) \).
- Distribute: \( 2(1) + 2(-2i) + 3i(1) + 3i(-2i) \)
- Simplify: \( 2 - 4i + 3i - 6i^2 \)
- Since \(i^2 = -1\): \( 2 - 4i + 3i + 6 = 8 - i \)
- Result: \( 8 - i \)
1.2 Polynomials
A polynomial is an expression consisting of variables (also called indeterminates) and coefficients, involving operations of addition, subtraction, multiplication, and non-negative integer exponents of variables.
Key Concepts:
- Degree: The highest exponent in the polynomial (e.g., the degree of \(2x^3 + 3x^2 - x + 5\) is 3).
- Factoring: Methods include factoring out the GCF, factoring trinomials, and using special products like the difference of squares.
- Polynomial Division: Two methods are long division and synthetic division.
Example 1: Factoring
Factor the polynomial \(4x^3 - 8x^2 + 16x\).
- Factor out the GCF: \(4x(x^2 - 2x + 4)\)
- Result: \(4x(x^2 - 2x + 4)\)
Example 2: Polynomial Division
Divide \(x^3 + 2x^2 - 5x - 6\) by \(x - 2\) using synthetic division.
- Set up the synthetic division using the zero of \(x - 2\) (which is 2).
- Perform the synthetic division: The quotient is \(x^2 + 4x + 3\) and the remainder is 0.
- Result: \(x^3 + 2x^2 - 5x - 6 = (x - 2)(x^2 + 4x + 3)\)
1.3 Functions and Their Properties
A function is a relation between a set of inputs (domain) and a set of possible outputs (range) where each input is related to exactly one output.
Key Concepts:
- Domain: The set of all possible input values (x-values).
- Range: The set of all possible output values (y-values).
- Transformations: Includes translations (shifts), reflections, and stretches/compressions.
Example:
Find the domain and range of the function \(f(x) = \frac{1}{x-2}\).
- Domain: Set the denominator equal to zero and solve for \(x\): \(x - 2 = 0 \Rightarrow x = 2\). The domain is all real numbers except 2, so \(x \neq 2\).
- Range: Since the function is undefined at \(x = 2\), the range is all real numbers except 0.
- Result: Domain: \(x \in \mathbb{R}, x \neq 2\). Range: \(f(x) \in \mathbb{R}, f(x) \neq 0\).
2. Equations and Inequalities
2.1 Quadratic Equations
A quadratic equation is a second-degree polynomial equation of the form \(ax^2 + bx + c = 0\).
Solving Methods:
- Factoring: Express the quadratic as a product of binomials.
- Quadratic Formula: Use the formula \(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\) to find the roots.
- Completing the Square: Rewrite the quadratic in the form \((x + p)^2 = q\) and solve.
Discriminant: The expression \(b^2 - 4ac\) indicates the nature of the roots:
- If \(b^2 - 4ac > 0\), there are two distinct real roots.
- If \(b^2 - 4ac = 0\), there is one real root (a repeated root).
- If \(b^2 - 4ac < 0\), there are two complex roots.
Example:
Solve the quadratic equation \(x^2 + 4x + 3 = 0\) by factoring.
- Factor the quadratic: \((x + 3)(x + 1) = 0\)
- Set each factor equal to zero and solve for \(x\): \(x + 3 = 0 \Rightarrow x = -3\), \(x + 1 = 0 \Rightarrow x = -1\)
- Result: \(x = -3\), \(x = -1\)
2.2 Rational Equations
Rational equations involve fractions with polynomials in the numerator and denominator.
Steps to Solve:
- Find a common denominator and multiply both sides by it to eliminate the fractions.
- Simplify and solve the resulting polynomial equation.
- Check for extraneous solutions by substituting back into the original equation.
Asymptotes: Identify vertical, horizontal, and slant asymptotes based on the degree of the numerator and denominator.
Example:
Solve the rational equation \( \frac{2x}{x - 3} = \frac{4}{x + 2} \).
- Cross-multiply to eliminate the fractions: \(2x(x + 2) = 4(x - 3)\)
- Expand and simplify: \(2x^2 + 4x = 4x - 12\)
- Subtract \(4x\) from both sides: \(2x^2 = -12\)
- Divide by 2: \(x^2 = -6\)
- Result: No real solutions (since \(x^2\) cannot be negative).
2.3 Exponential and Logarithmic Equations
Exponential equations have the form \(a^x = b\), and logarithmic equations have the form \(\log_b(x) = y\).
Key Properties:
- \(a^m \cdot a^n = a^{m+n}\)
- \((a^m)^n = a^{mn}\)
- \(\log_b(mn) = \log_b(m) + \log_b(n)\)
- \(\log_b\left(\frac{m}{n}\right) = \log_b(m) - \log_b(n)\)
Solving Steps:
- For exponential equations, take the logarithm of both sides.
- For logarithmic equations, exponentiate both sides to remove the logarithm.
- Simplify and solve for the variable.
Example 1: Exponential Equation
Solve \(3^{2x + 1} = 81\).
- Rewrite 81 as a power of 3: \(81 = 3^4\)
- Set the exponents equal: \(2x + 1 = 4\)
- Solve for \(x\): \(2x = 3 \Rightarrow x = \frac{3}{2}\)
- Result: \(x = \frac{3}{2}\)
Example 2: Logarithmic Equation
Solve \(\log_2(x + 3) = 4\).
- Rewrite the equation in exponential form: \(2^4 = x + 3\)
- Solve for \(x\): \(x = 16 - 3 = 13\)
- Result: \(x = 13\)
3. Functions
3.1 Linear Functions
A linear function is a function of the form \(y = mx + b\), where \(m\) is the slope and \(b\) is the y-intercept.
Key Forms:
- Slope-Intercept Form: \(y = mx + b\)
- Point-Slope Form: \(y - y_1 = m(x - x_1)\), where \((x_1, y_1)\) is a point on the line.
Example:
Find the equation of a line with slope 3 passing through the point (2, -1).
- Use the point-slope form: \(y - (-1) = 3(x - 2)\)
- Simplify: \(y + 1 = 3x - 6\)
- Subtract 1 from both sides: \(y = 3x - 7\)
- Result: \(y = 3x - 7\)
3.2 Quadratic Functions
A quadratic function is a function of the form \(y = ax^2 + bx + c\). It graphs as a parabola.
Key Forms:
- Standard Form: \(y = ax^2 + bx + c\)
- Vertex Form: \(y = a(x - h)^2 + k\), where (h, k) is the vertex of the parabola.
- Factored Form: \(y = a(x - r_1)(x - r_2)\), where \(r_1\) and \(r_2\) are the roots of the quadratic.
Example:
Convert the quadratic function \(y = 2x^2 + 8x + 5\) to vertex form.
- Factor out the coefficient of \(x^2\): \(y = 2(x^2 + 4x) + 5\)
- Complete the square: \(y = 2(x^2 + 4x + 4) - 8 + 5\)
- Simplify: \(y = 2(x + 2)^2 - 3\)
- Result: \(y = 2(x + 2)^2 - 3\)
3.3 Polynomial Functions
Polynomial functions are functions that are represented by polynomials. The degree of the polynomial determines the behavior of the graph at the ends (end behavior).
Key Concepts:
- End Behavior: The direction the graph moves as \(x\) approaches positive or negative infinity.
- Factoring and Roots: The roots of the polynomial correspond to the x-intercepts of the graph.
- The Fundamental Theorem of Algebra: Every polynomial equation of degree \(n\) has exactly \(n\) roots (counting multiplicities).
Example:
Determine the end behavior of the polynomial function \(f(x) = -2x^3 + 3x^2 - x + 1\).
- The leading term is \(-2x^3\), which dominates the behavior as \(x\) becomes large.
- As \(x \rightarrow +\infty\), \(f(x) \rightarrow -\infty\).
- As \(x \rightarrow -\infty\), \(f(x) \rightarrow +\infty\).
- Result: The end behavior is:
- \(\lim_{x \rightarrow +\infty} f(x) = -\infty\)
- \(\lim_{x \rightarrow -\infty} f(x) = +\infty\)
3.4 Rational Functions
Rational functions are functions of the form \(f(x) = \frac{p(x)}{q(x)}\), where \(p(x)\) and \(q(x)\) are polynomials and \(q(x) \neq 0\).
Asymptotes:
- Vertical Asymptotes: Occur where \(q(x) = 0\), and the function approaches infinity.
- Horizontal Asymptotes: Determined by the degrees of \(p(x)\) and \(q(x)\). If the degree of the numerator is less than the degree of the denominator, the horizontal asymptote is \(y = 0\).
- Slant Asymptotes: Occur when the degree of the numerator is one more than the degree of the denominator.
Example:
Identify the vertical and horizontal asymptotes of the function \(f(x) = \frac{x^2 - 1}{x - 2}\).
- Vertical asymptote: Set \(x - 2 = 0 \Rightarrow x = 2\).
- Horizontal asymptote: Since the degree of the numerator is greater than the degree of the denominator, there is no horizontal asymptote.
- Result: Vertical asymptote at \(x = 2\). No horizontal asymptote.
3.5 Exponential and Logarithmic Functions
Exponential functions have the form \(f(x) = a \cdot b^x\), where \(a\) and \(b\) are constants, and \(b > 0\). Logarithmic functions are the inverse of exponential functions and have the form \(f(x) = \log_b(x)\).
Graphing:
- Exponential functions have a horizontal asymptote and increase or decrease rapidly.
- Logarithmic functions have a vertical asymptote and increase or decrease slowly.
Example 1: Exponential Function
Graph \(f(x) = 2^x\).
- Identify the horizontal asymptote: \(y = 0\).
- Plot points: \(f(0) = 1\), \(f(1) = 2\), \(f(-1) = \frac{1}{2}\).
- Draw the graph: The curve passes through the points and approaches the asymptote.
Example 2: Logarithmic Function
Graph \(f(x) = \log_2(x)\).
- Identify the vertical asymptote: \(x = 0\).
- Plot points: \(f(1) = 0\), \(f(2) = 1\), \(f(\frac{1}{2}) = -1\).
- Draw the graph: The curve passes through the points and approaches the asymptote.
4. Sequences and Series
4.1 Arithmetic Sequences
An arithmetic sequence is a sequence of numbers in which the difference between consecutive terms is constant. The general term of an arithmetic sequence is given by \(a_n = a_1 + (n - 1)d\), where \(a_1\) is the first term and \(d\) is the common difference.
Sum of n Terms:
- The sum of the first \(n\) terms of an arithmetic sequence is \(S_n = \frac{n}{2}(a_1 + a_n)\).
Example:
Find the sum of the first 20 terms of the arithmetic sequence 2, 5, 8, ...
- Identify \(a_1 = 2\) and \(d = 3\).
- Find the 20th term: \(a_{20} = 2 + (20 - 1) \cdot 3 = 2 + 57 = 59\).
- Use the sum formula: \(S_{20} = \frac{20}{2}(2 + 59) = 10 \cdot 61 = 610\).
- Result: The sum of the first 20 terms is 610.
4.2 Geometric Sequences
A geometric sequence is a sequence of numbers where each term after the first is found by multiplying the previous term by a fixed, non-zero number called the common ratio. The general term of a geometric sequence is given by \(a_n = a_1 \cdot r^{(n-1)}\), where \(a_1\) is the first term and \(r\) is the common ratio.
Sum of n Terms:
- The sum of the first \(n\) terms of a geometric sequence is \(S_n = a_1 \frac{1 - r^n}{1 - r}\) for \(r \neq 1\).
Example:
Find the sum of the first 5 terms of the geometric sequence 3, 6, 12, ...
- Identify \(a_1 = 3\) and \(r = 2\).
- Use the sum formula: \(S_5 = 3 \frac{1 - 2^5}{1 - 2} = 3 \frac{1 - 32}{-1} = 3 \cdot 31 = 93\).
- Result: The sum of the first 5 terms is 93.
4.3 Series
A series is the sum of the terms of a sequence. For arithmetic and geometric series, there are specific formulas to calculate the sum of the first \(n\) terms.
Infinite Geometric Series:
- An infinite geometric series converges to \(S = \frac{a_1}{1 - r}\) if \(|r| < 1\).
Example:
Find the sum of the infinite geometric series \( \frac{1}{3} + \frac{1}{9} + \frac{1}{27} + \dots \)
- Identify \(a_1 = \frac{1}{3}\) and \(r = \frac{1}{3}\).
- Use the sum formula: \(S = \frac{\frac{1}{3}}{1 - \frac{1}{3}} = \frac{\frac{1}{3}}{\frac{2}{3}} = \frac{1}{2}\).
- Result: The sum of the series is \( \frac{1}{2} \).
5. Conic Sections
5.1 Parabolas
A parabola is the graph of a quadratic function. The standard form of a parabola is \(y = ax^2 + bx + c\) or \(x = ay^2 + by + c\).
Vertex Form:
- The vertex form of a parabola is \(y = a(x - h)^2 + k\), where (h, k) is the vertex.
Example:
Find the vertex of the parabola \(y = 2x^2 - 8x + 6\).
- Rewrite the equation in vertex form by completing the square: \(y = 2(x^2 - 4x) + 6\).
- Complete the square: \(y = 2(x - 2)^2 - 2\).
- The vertex is at (2, -2).
- Result: The vertex is (2, -2).
5.2 Circles
A circle is a set of all points in a plane that are equidistant from a fixed point called the center. The standard form of the equation of a circle is \((x - h)^2 + (y - k)^2 = r^2\), where (h, k) is the center and \(r\) is the radius.
Example:
Write the equation of a circle with center at (3, -2) and radius 5.
- Use the standard form: \((x - 3)^2 + (y + 2)^2 = 25\).
- Result: \((x - 3)^2 + (y + 2)^2 = 25\).
5.3 Ellipses
An ellipse is a set of all points in a plane where the sum of the distances from two fixed points (the foci) is constant. The standard form of an ellipse is \(\frac{(x - h)^2}{a^2} + \frac{(y - k)^2}{b^2} = 1\), where (h, k) is the center, \(a\) is the distance from the center to a vertex along the major axis, and \(b\) is the distance from the center to a vertex along the minor axis.
Example:
Write the equation of an ellipse with center at (0, 0), a major axis of length 10 along the x-axis, and a minor axis of length 6 along the y-axis.
- The equation is \(\frac{x^2}{25} + \frac{y^2}{9} = 1\).
- Result: \(\frac{x^2}{25} + \frac{y^2}{9} = 1\).
5.4 Hyperbolas
A hyperbola is a set of all points in a plane where the difference of the distances from two fixed points (the foci) is constant. The standard form of a hyperbola is \(\frac{(x - h)^2}{a^2} - \frac{(y - k)^2}{b^2} = 1\) (horizontal hyperbola) or \(\frac{(y - k)^2}{a^2} - \frac{(x - h)^2}{b^2} = 1\) (vertical hyperbola).
Asymptotes: The asymptotes of a hyperbola are the lines that the hyperbola approaches but never touches. For a hyperbola centered at (h, k), the asymptotes are given by the equations \(y - k = \pm \frac{b}{a}(x - h)\) (horizontal hyperbola) or \(y - k = \pm \frac{a}{b}(x - h)\) (vertical hyperbola).
Example:
Write the equation of a hyperbola with center at (1, -2), a horizontal transverse axis, \(a = 4\), and \(b = 3\).
- The equation is \(\frac{(x - 1)^2}{16} - \frac{(y + 2)^2}{9} = 1\).
- Result: \(\frac{(x - 1)^2}{16} - \frac{(y + 2)^2}{9} = 1\).