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.

7a⁶ - 8a⁶ = -1a⁶

To factor a quadratic expression, apply the FOIL method (First, Outside, Inside, Last) in reverse. First, find the two Last terms that will multiply to produce 42 as well and sum (Inside, Outside) to equal -13. For this problem, those two numbers are -7 and -6. Then, plug these into a set of binomials using the square root of the First variable (y²):

y² - 13y + 42
y² + (-7 - 6)y + (-7 x -6)
(y - 7)(y - 6)

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 < sign and the answer on the other.

5z - 2 < -8 + 2z
5z < -8 + 2z + 2
5z - 2z < -8 + 2
3z < -6
z < \( \frac{-6}{3} \)
z < -2

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 sum of the interior angles of a triangle is 180°:
180° = a° + b° + c°
c° = 180° - a° - b°
c° = 180° - 64° - 70° = 46°