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ACT Math Concepts

From Kaplan's 100 Key Math Concepts for the ACT - the ones that I didn't know :D

Undefined Numbers on the ACT, almost always means division by zero
Imaginary Numbers on the ACT, almost always means numbers that involve the square root of a negative number
How do you solve a rates problem? By using a proportion.
What is the trick to finding the average of evenly spaced numbers? Average the smallest and the largest numbers.
How do you find possibilities? Multiply the different elements factoring into the possibility by each other.
How do you solve a system of equations Multiply one of the equations so that when added to the other equation, either x or y cancels out.
What is slope intercept form? y=mx+b
How do you find the slope-intercept of y or x? Plug x or y (respectively) into the equation and solve.
What is the equation for a circle? (x-h)^2 + (y-k)^2 = r^2
Name the two special right triangles that correspond with the length of the legs. 3-4-5 and 5-12-13
The sides of a 30°-60°-90° triangle are in a ratio of.... 1:√3:2
The sides of a 45°-45°-90° triangle are in a ratio of.... 1:1:√2
Formula for the area of a trapezoid (b1+b2/2)xh
The fundamental trigonometric identity: sin^2x + cos^2x=1
Created by: Teens