A circle is a figure in which each point around its perimeter is an equal distance from the center. The radius of a circle is the distance between the center and any point along its perimeter. A chord is a line segment that connects any two points along its perimeter. The diameter of a circle is the length of a chord that passes through the center of the circle and equals twice the circle's radius (2r).

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

b² + 7b - 18 = 0
(b - 2)(b + 9) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (b - 2) or (b + 9) must equal zero:

If (b - 2) = 0, b must equal 2
If (b + 9) = 0, b must equal -9

So the solution is that b = 2 or -9

A parallelogram is a quadrilateral with two sets of parallel sides. Opposite sides (a = c, b = d) and angles (red = red, blue = blue) are equal. The area of a parallelogram is base x height and the perimeter is the sum of the lengths of all sides (a + b + c + d).

To combine like terms, add or subtract the coefficients (the numbers that come before the variables) of terms that have the same variable raised to the same exponent.

8a - 4a = 4a