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

sa = 2πr² + 2πrh
sa = 2π(2²) + 2π(2 x 4)
sa = 2π(4) + 2π(8)
sa = (2 x 4)π + (2 x 8)π
sa = 8π + 16π
sa = 24π

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

b² - 9 = 0
(b - 3)(b + 3) = 0

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

If (b - 3) = 0, b must equal 3
If (b + 3) = 0, b must equal -3

So the solution is that b = 3 or -3

Angles around a line add up to 180°. Angles around a point add up to 360°. When two lines intersect, adjacent angles are supplementary (they add up to 180°) and angles across from either other are vertical (they're equal).

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.

-8c + 4 < \( \frac{c}{-8} \)
-8 x (-8c + 4) < c
(-8 x -8c) + (-8 x 4) < c
64c - 32 < c
64c - 32 - c < 0
64c - c < 32
63c < 32
c < \( \frac{32}{63} \)
c < \(\frac{32}{63}\)

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.

(7a)(3ab) - (5a²)(5b)
(7 x 3)(a x a x b) - (5 x 5)(a² x b)
(21)(a¹⁺¹ x b) - (25)(a²b)
21a²b - 25a²b
-4a²b