Math · Study Guide
ACT Math Formulas You Must Memorize
A short list of the formulas that show up on every ACT — keep them on a notecard until they are second nature.
Geometry
Area of a triangle = ½ × base × height. Area of a circle = πr². Circumference = 2πr. Pythagorean theorem: a² + b² = c². Special right triangles: 30-60-90 has sides in ratio 1:√3:2; 45-45-90 has sides in ratio 1:1:√2.
Coordinate Geometry
Slope = (y₂ - y₁)/(x₂ - x₁). Slope-intercept form: y = mx + b. Distance formula: √((x₂ - x₁)² + (y₂ - y₁)²). Midpoint: ((x₁ + x₂)/2, (y₁ + y₂)/2).
Trigonometry
SOHCAHTOA: sin = opp/hyp, cos = adj/hyp, tan = opp/adj. Pythagorean identity: sin²θ + cos²θ = 1. Special angles: sin 30° = ½, sin 45° = √2/2, sin 60° = √3/2.
What to do next
Write these on a notecard and review them once a day for a week. By the test, they should be muscle memory.
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