To solve this equation, 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.)

6c(c - y)
6(-2)(-2 + 7)
6(-2)(5)
(-12)(5)
-60

To factor a quadratic expression, apply the FOIL method (First, Outside, Inside, Last) in reverse. First, find the two Last terms that will multiply to produce -8 as well and sum (Inside, Outside) to equal -2. For this problem, those two numbers are -4 and 2. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² - 2y - 8
y² + (-4 + 2)y + (-4 x 2)
(y - 4)(y + 2)

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° - 51° - 45° = 84°

So, d° = 45° + 84° = 129°

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° - 51° = 129°

The circumference of a circle is the distance around its perimeter and equals π (approx. 3.14159) x diameter: c = π d. The area of a circle is π x (radius)² : a = π r².

To multiply monomials, multiply the coefficients (the numbers that come before the variables) of each term, add the exponents of like variables, and multiply the different variables together.

(2a)(9ab) + (2a²)(7b)
(2 x 9)(a x a x b) + (2 x 7)(a² x b)
(18)(a¹⁺¹ x b) + (14)(a²b)
18a²b + 14a²b
32a²b