Algebra is about a third of the Math section, and every question uses a line, an equation or an inequality. You will solve, build and interpret linear models, often from a short story. Most points come from fast, accurate setup: know slope, intercepts and how a system's lines meet.
- linear equation in one variable
- An equation that can be written ax + b = c with a ≠ 0. Isolate x to get x = (c − b)/a.
- Example: 3x + 5 = 20 → 3x = 15 → x = 5.
- linear equation in two variables
- An equation such as Ax + By = C. A solution is an ordered pair (x, y) that makes it true.
- Example: For 2x + y = 7, the pair (3, 1) works because 6 + 1 = 7.
- function
- A rule that assigns each input exactly one output.
- Example: x = y² doesn't make y a function of x: input x = 4 gives y = 2 and y = −2.
- system of linear equations
- Two equations solved together. A solution (x, y) must satisfy both equations.
- Example: x + y = 7 and x − y = 3 hold at (5, 2) only.
- linear inequality in one variable
- Solved like an equation, but the answer is a range of values, shown on a number line.
- Example: 2x + 1 < 9 → 2x < 8 → x < 4.
- properties of equality
- Adding or subtracting the same number on both sides, or multiplying or dividing both sides by the same nonzero number, keeps the solutions the same.
- Example: x − 4 = 9: add 4 to both sides, so x = 13.
- slope
- Rise over run: m = (y₂ − y₁)/(x₂ − x₁). Positive slopes rise left to right; negative slopes fall.
- Example: From (1, 2) to (3, 8) the graph rises 6 while moving right 2: m = 3.
- function notation
- f(x) names the output for input x. To evaluate f(3), substitute 3 for x. A coefficient multiplies the output: 4f(2) is 4 × f(2), not f(8).
- Example: f(x) = 4x − 3: f(3) = 9, so 2f(3) = 2 × 9 = 18, not f(6) = 21.
- substitution method
- Solve one equation for a variable, then substitute that expression into the other equation.
- Example: y = 2x and x + y = 9: x + 2x = 9, so x = 3 and y = 6.
- reversing the inequality sign
- Multiplying or dividing both sides by a negative number flips the inequality sign.
- Example: −2x > 10 → x < −5.
- distributive property and combining like terms
- a(b + c) = ab + ac. Then add or subtract terms that have the same variable part.
- Example: 2(x + 3) + 4x = 2x + 6 + 4x = 6x + 6.
- slope-intercept form
- y = mx + b, where m is the slope and b is the y-intercept.
- Example: y = −2x + 5 has slope −2 and crosses the y-axis at (0, 5).