ACT Math: Formulas Key Concepts 2026. Exam Questions and Correct
Answers With 100% Correct Answers | Latest 2026 |
Vertical Angles - Formed by 2 intersecting lines or segments. Always congruent.
Supplementary Angles - Two angles that form a line and add up to 180°.
Right Angle - An angle that measures 90°.
Complimentary Angles - Two angles that add up to 90°.
Alternate Interior Angles (Parallel Lines) - Ex. 3 & 6 are congruent
Alternate Exterior Angles (Parallel Lines) - Ex. 1 & 8 are congruent
Corresponding Angles (Parallel Lines) - Ex. 1 & 5 are congruent
Same Side Interior Angles (Parallel Lines) - Ex. 3 & 5 add up to 180º
Area of a Triangle - A=½(Base)(Height)
A=½bh
Triangle Inequality Theorem - The sum of the 2 shortest sides of a triangle is always greater
than the length of the third side.
Equilateral Triangle - A triangle in which all three sides are equal and all three interior
angles are 60°.
, Isosceles Triangle - A triangle with two equal sides. Base angles (angles across from the
congruent sides) are also equal.
Proportionality in Triangles - In every triangle, the longest side is opposite the largest angle
and the smallest side is opposite the smallest angle.
Pythagorean Theorem - Used to find the missing side of a right triangle.
"c" is always the length of the hypotenuse.
a²+b²=c²
Similar Triangles - Triangles that have the same angle measures but different side lengths.
Solve by setting up a proportion.
45-45-90 Special Triangle - Always in the ratio 1:1:√2
Isosceles right triangle
30-60-90 Special Triangle - Always in the ratio 1:√3:2
Pythagorean Triple - Three integers that, as side lengths of a triangle, form a right triangle.
Ex. 3/4/5 or 5/12/13
Degree Measure of a Triangle - The inside angles of a triangle always add up to 180°.
Area of a Circle - A=πr²
Degree Measure of a Circle - The central angles of a circle add up to 360°.
Answers With 100% Correct Answers | Latest 2026 |
Vertical Angles - Formed by 2 intersecting lines or segments. Always congruent.
Supplementary Angles - Two angles that form a line and add up to 180°.
Right Angle - An angle that measures 90°.
Complimentary Angles - Two angles that add up to 90°.
Alternate Interior Angles (Parallel Lines) - Ex. 3 & 6 are congruent
Alternate Exterior Angles (Parallel Lines) - Ex. 1 & 8 are congruent
Corresponding Angles (Parallel Lines) - Ex. 1 & 5 are congruent
Same Side Interior Angles (Parallel Lines) - Ex. 3 & 5 add up to 180º
Area of a Triangle - A=½(Base)(Height)
A=½bh
Triangle Inequality Theorem - The sum of the 2 shortest sides of a triangle is always greater
than the length of the third side.
Equilateral Triangle - A triangle in which all three sides are equal and all three interior
angles are 60°.
, Isosceles Triangle - A triangle with two equal sides. Base angles (angles across from the
congruent sides) are also equal.
Proportionality in Triangles - In every triangle, the longest side is opposite the largest angle
and the smallest side is opposite the smallest angle.
Pythagorean Theorem - Used to find the missing side of a right triangle.
"c" is always the length of the hypotenuse.
a²+b²=c²
Similar Triangles - Triangles that have the same angle measures but different side lengths.
Solve by setting up a proportion.
45-45-90 Special Triangle - Always in the ratio 1:1:√2
Isosceles right triangle
30-60-90 Special Triangle - Always in the ratio 1:√3:2
Pythagorean Triple - Three integers that, as side lengths of a triangle, form a right triangle.
Ex. 3/4/5 or 5/12/13
Degree Measure of a Triangle - The inside angles of a triangle always add up to 180°.
Area of a Circle - A=πr²
Degree Measure of a Circle - The central angles of a circle add up to 360°.
