A rectangle is a parallelogram containing four right angles. Opposite sides (a = c, b = d) are equal and the perimeter is the sum of the lengths of all sides (a + b + c + d) or, comonly, 2 x length x width. The area of a rectangle is length x width. A square is a rectangle with four equal length sides. The perimeter of a square is 4 x length of one side (4s) and the area is the length of one side squared (s²).

To multiply monomials, multiply the coefficients (the numbers that come before the variables) of each term, add the exponents of like variables, and multiply the different variables together.

8a x 2b = (8 x 2) (a x b) = 16ab

The circumference of a circle is the distance around its perimeter and equals π (approx. 3.14159) x diameter: c = π d. The area of a circle is π x (radius)² : a = π r².

The area of a parallelogram is equal to its length x width:

a = l x w
a = a x b
a = 8 x 9
a = 72

The first step to solve a quadratic expression that's not set to zero is to solve the equation so that it is set to zero:

c² - 4c - 1 = -4c + 3
c² - 4c - 1 - 3 = -4c
c² - 4c + 4c - 4 = 0
c² - 4 = 0

Next, factor the quadratic equation:

c² - 4 = 0
(c - 2)(c + 2) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (c - 2) or (c + 2) must equal zero:

If (c - 2) = 0, c must equal 2
If (c + 2) = 0, c must equal -2

So the solution is that c = 2 or -2