An equation is two expressions separated by an equal sign. The key to solving equations is to repeatedly do the same thing to both sides of the equation until the variable is isolated on one side of the equal sign and the answer on the other.

The area of a trapezoid is one-half the sum of the lengths of the parallel sides multiplied by the height:

a = ½(b + d)(h)
a = ½(8 + 5)(4)
a = ½(13)(4)
a = ½(52) = \( \frac{52}{2} \)
a = 26

The perimeter of a triangle is the sum of the lengths of its sides:

p = x + y + z
p = 15cm + 13cm + 11cm = 39cm

To factor a quadratic expression, apply the FOIL method (First, Outside, Inside, Last) in reverse. First, find the two Last terms that will multiply to produce -12 as well and sum (Inside, Outside) to equal -1. For this problem, those two numbers are -4 and 3. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² - y - 12
y² + (-4 + 3)y + (-4 x 3)
(y - 4)(y + 3)

A rhombus is a parallelogram with four equal-length sides. A square is a rectangle with four equal-length sides.