Parallel lines are lines that share the same slope (steepness) and therefore never intersect. A transversal occurs when a set of parallel lines are crossed by another line. All of the angles formed by a transversal are called interior angles and angles in the same position on different parallel lines equal each other (a° = w°, b° = x°, c° = z°, d° = y°) and are called corresponding angles. Alternate interior angles are equal (a° = z°, b° = y°, c° = w°, d° = x°) and all acute angles (a° = c° = w° = z°) and all obtuse angles (b° = d° = x° = y°) equal each other. Same-side interior angles are supplementary and add up to 180° (e.g. a° + d° = 180°, d° + c° = 180°).

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

x² - 4x - 21 = 0
(x + 3)(x - 7) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (x + 3) or (x - 7) must equal zero:

If (x + 3) = 0, x must equal -3
If (x - 7) = 0, x must equal 7

So the solution is that x = -3 or 7

A trapezoid is a quadrilateral with one set of parallel 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.

7a⁸ - 8a⁸ = -1a⁸

To solve this equation, 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.

-8b - 4 = -7 - 6b
-8b = -7 - 6b + 4
-8b + 6b = -7 + 4
-2b = -3
b = \( \frac{-3}{-2} \)
b = 1\(\frac{1}{2}\)