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 + 2)(y - 7)
(y x y) + (y x -7) + (2 x y) + (2 x -7)
y² - 7y + 2y - 14
y² - 5y - 14

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.

9a + 8a = 17a

An exterior angle of a triangle is equal to the sum of the two interior angles that are opposite:

d° = b° + c°

To find angle c, remember that the sum of the interior angles of a triangle is 180°:

180° = a° + b° + c°
c° = 180° - a° - b°
c° = 180° - 22° - 68° = 90°

So, d° = 68° + 90° = 158°

A shortcut to get this answer is to remember that angles around a line add up to 180°:

a° + d° = 180°
d° = 180° - a°
d° = 180° - 22° = 158°

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

a² - 4a - 5 = 0
(a + 1)(a - 5) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (a + 1) or (a - 5) must equal zero:

If (a + 1) = 0, a must equal -1
If (a - 5) = 0, a must equal 5

So the solution is that a = -1 or 5

An acute angle measures less than 90°, a right angle measures 90°, and an obtuse angle measures more than 90°.