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.

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 + 2a = 6a

To multiply monomials, multiply the coefficients (the numbers that come before the variables) of each term, add the exponents of like variables, and multiply the different variables together.

(6a)(5ab) + (2a²)(4b)
(6 x 5)(a x a x b) + (2 x 4)(a² x b)
(30)(a¹⁺¹ x b) + (8)(a²b)
30a²b + 8a²b
38a²b

The surface area of a cylinder is 2πr² + 2πrh:

sa = 2πr² + 2πrh
sa = 2π(3²) + 2π(3 x 9)
sa = 2π(9) + 2π(27)
sa = (2 x 9)π + (2 x 27)π
sa = 18π + 54π
sa = 72π

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 equal sign and the answer on the other.

-6z + 2 = 6 - 4z
-6z = 6 - 4z - 2
-6z + 4z = 6 - 2
-2z = 4
z = \( \frac{4}{-2} \)
z = -2