GRE Math Formulas and Definitions
Terms
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1. Write prime factors out
2. Cross out any PF in second denom. that appears in first denom
3. Multiply remaining factors 
Averages:
Mean
Median
Mode 
Mean: Sum of #s/ # of elements
Median: Middle
Mode: Most often  Average of X #s = Y...

X = number of elements
Y = the average
Therefore, if sum/X = Y
Sum = XY  Ratio/Proportion

Ratio compares 2 #s
Proportion two equal ratios 
(X)^2,4,6,8,10...
(X)^1,3,5,9... 
Even power Always positive
Odd power Always negative  Binomial Squares
 FOIL First, Outer, Inner, Last
 Linear Equation

Highest power of any variable is 1
Solve by isolating variable on 1 side  Quadratic Equation

At least one variable is raised to 2nd power
Set one side of equation = 0
Factor out nonzero side
Set each Factor = 0 and solve  Area of Triangle
 A = 1/2bh
 Rectangle Area, Perimeter

A = lw
P = 2l + 2w  Circle

A = Pi r^2
C = Pi d or 2Pi r  Length of Arc
 Arc AB = (X/360) x 2Pi r
 Pi
 3.14 or 22/7
 Inscribed Angle
 1/2 measure of intercepted Arc
 Surface Area of a Cube
 S = 6a^2
 Volume, SA

V = lwh
SA = sum of areas of all faces  Distance

d =
Radical( x1x2)^2 + (y1y2)^2  Midpoint

MP =
__x1+x2__ , __y1+y2__
2 2  Slope

__y1y2__
x1x2
if (x1 does NOT = x2)  Fraction Denominatiors
 Denominator decreases as Value increases
 Algebraic expressions
 Factor, Rearrange, Multiply Out