A quadrilateral is a shape with four sides. The perimeter of a quadrilateral is the sum of the lengths of its four sides.

The first step to solve a quadratic equation that's set to zero is to factor the quadratic equation:

z² + 10z + 9 = 0
(z + 1)(z + 9) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (z + 1) or (z + 9) must equal zero:

If (z + 1) = 0, z must equal -1
If (z + 9) = 0, z must equal -9

So the solution is that z = -1 or -9

When solving an equation with two variables, replace the variables with the values given and then solve the now variable-free equation. (Remember order of operations, PEMDAS, Parentheses, Exponents, Multiplication/Division, Addition/Subtraction.)

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 rectangle is equal to its length x width:

a = l x w
a = a x b
a = 5 x 6
a = 30