GRE Math Fact V.2

In a set of n numbers arranged in an increasing order, the median is the middle number (if n is odd), or the average of the two middle numbers (if n is even).

The mode is the number that appears most often.

• Memorize these three binomial products:
• (x+y)(x-y) = x² -y²
• (x+y)² = (x+y)(x+y) = x² + 2xy + y²
• (x-y)² = (x-y)(x-y) = x² -2xy + y²

The measure of a straight angle is 180^o . If two or more angles form a straight angle, the sum of their measure is 180^o .

No matter how many angles there are, the sum of the measures of all the angles around a point is 360^o .

When the two lines intersect, two pairs of opposite or vertical angles are formed. In each pair the two angles are equal.

In any triangle, the sum of the measures of the three angles is 180^o .

• In any triangle:
• The longest side is opposite the largest angle.
• The shortest side is opposite the smallest angle.
• Sides with the same length are opposite angles with the same measure.

The Pythagorean theorm states that in a right triangle. the sum of the squares of the two legs is equal to the square of the length of the hypotenuse.

a² + b² = c²

The formual for the area of a triangle is A = 1/2bh. Where b is the base and h is the height.

If two triangles are similar, the ratio of their corresponding sides is called the ratio of similitude. In those triangles, the ratio of all corresponding linear measurements are equal to the ratio of similitude.

If two triangles are similar with a ratio of similitude of k, the ratio of their areas is k² .

π = 3.14159

• In a circle of radius r:
• The diameter is twice the radius: d = 2r
• The circumference is π times the diameter: C = πd.
• THe area of the circle is: A = π r² .

slope = y₂ - y₁ / x₂ - x₁

• If E represents any event, the probability that E will occur is:
• P(E) = number of favorable outcomes / total number of possible outcomes.