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

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.

5a⁷ - 7a⁷ = -2a⁷

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).

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

x² - 25 = 0
(x - 5)(x + 5) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (x - 5) or (x + 5) must equal zero:

If (x - 5) = 0, x must equal 5
If (x + 5) = 0, x must equal -5

So the solution is that x = 5 or -5

The surface area of a cube is (2 x length x width) + (2 x width x height) + (2 x length x height):

sa = 2lw + 2wh + 2lh
sa = (2 x 9 x 6) + (2 x 6 x 7) + (2 x 9 x 7)
sa = (108) + (84) + (126)
sa = 318