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.

2a + 4a = 6a

A rectangle is a parallelogram containing four right angles. Opposite sides (a = c, b = d) are equal and the perimeter is the sum of the lengths of all sides (a + b + c + d) or, comonly, 2 x length x width. The area of a rectangle is length x width. A square is a rectangle with four equal length sides. The perimeter of a square is 4 x length of one side (4s) and the area is the length of one side squared (s²).

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

A circle is a figure in which each point around its perimeter is an equal distance from the center. The radius of a circle is the distance between the center and any point along its perimeter. A chord is a line segment that connects any two points along its perimeter. The diameter of a circle is the length of a chord that passes through the center of the circle and equals twice the circle's radius (2r).

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

x² - 6x + 8 = 0
(x - 2)(x - 4) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (x - 2) or (x - 4) must equal zero:

If (x - 2) = 0, x must equal 2
If (x - 4) = 0, x must equal 4

So the solution is that x = 2 or 4