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.)

2a(a - x)
2(1)(1 + 2)
2(1)(3)
(2)(3)
6

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.

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

c² + 9c + 8 = 0
(c + 1)(c + 8) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (c + 1) or (c + 8) must equal zero:

If (c + 1) = 0, c must equal -1
If (c + 8) = 0, c must equal -8

So the solution is that c = -1 or -8

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 2 x 7) + (2 x 7 x 2) + (2 x 2 x 2)
sa = (28) + (28) + (8)
sa = 64

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.

9a + 3 = -4 + 8a
9a = -4 + 8a - 3
9a - 8a = -4 - 3
a = -7