To multiply binomials, use the FOIL method. FOIL stands for First, Outside, Inside, Last and refers to the position of each term in the parentheses:

(y + 1)(y + 4)
(y x y) + (y x 4) + (1 x y) + (1 x 4)
y² + 4y + y + 4
y² + 5y + 4

For parallel lines with a transversal, the following relationships apply:

• angles in the same position on different parallel lines equal each other (a° = w°, b° = x°, c° = z°, d° = y°)
• alternate interior angles are equal (a° = z°, b° = y°, c° = w°, d° = x°)
• 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°)

Applying these relationships starting with c° = 15, the value of b° is 165.

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

x² - 13x + 36 = 0
(x - 4)(x - 9) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (x - 4) or (x - 9) must equal zero:

If (x - 4) = 0, x must equal 4
If (x - 9) = 0, x must equal 9

So the solution is that x = 4 or 9

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.

9a⁴ + 4a⁴ = 13a⁴

A right angle measures 90 degrees and is the intersection of two perpendicular lines. In diagrams, a right angle is indicated by a small box completing a square with the perpendicular lines.