A parallelogram is a quadrilateral with two sets of parallel sides. Opposite sides (a = c, b = d) and angles (red = red, blue = blue) are equal. The area of a parallelogram is base x height and the perimeter is the sum of the lengths of all sides (a + b + c + d).

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.

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

a² - 49 = 0
(a - 7)(a + 7) = 0

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

If (a - 7) = 0, a must equal 7
If (a + 7) = 0, a must equal -7

So the solution is that a = 7 or -7

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.

4a - 4a = 0a

The area of a parallelogram is equal to its length x width:

a = l x w
a = a x b
a = 8 x 2
a = 16