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

a = l x w
a = a x b
a = 2 x 5
a = 10

The first step to solve a quadratic expression that's not set to zero is to solve the equation so that it is set to zero:

a² - 7a - 19 = -4a - 1
a² - 7a - 19 + 1 = -4a
a² - 7a + 4a - 18 = 0
a² - 3a - 18 = 0

Next, factor the quadratic equation:

a² - 3a - 18 = 0
(a + 3)(a - 6) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (a + 3) or (a - 6) must equal zero:

If (a + 3) = 0, a must equal -3
If (a - 6) = 0, a must equal 6

So the solution is that a = -3 or 6

The formula for circumference is circle diameter x π. Circle diameter is 2 x radius:

c = πd
c = π(2 * r)
c = π(2 * 18)
c = 36π

When solving an equation with two variables, 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.)

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).