A rhombus is a parallelogram with four equal-length sides. A square is a rectangle with four equal-length sides.

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:

y² - 5y + 20 = 5y + 4
y² - 5y + 20 - 4 = 5y
y² - 5y - 5y + 16 = 0
y² - 10y + 16 = 0

Next, factor the quadratic equation:

y² - 10y + 16 = 0
(y - 2)(y - 8) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (y - 2) or (y - 8) must equal zero:

If (y - 2) = 0, y must equal 2
If (y - 8) = 0, y must equal 8

So the solution is that y = 2 or 8

To factor a quadratic expression, apply the FOIL (First, Outside, Inside, Last) method in reverse.

A trapezoid is a quadrilateral with one set of parallel sides.

A right angle measures 90 degrees and is the intersection of two perpendicular lines. In diagrams, a right angle is indicated by a small box completing a square with the perpendicular lines.