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

sa = 2πr² + 2πrh
sa = 2π(1²) + 2π(1 x 7)
sa = 2π(1) + 2π(7)
sa = (2 x 1)π + (2 x 7)π
sa = 2π + 14π
sa = 16π

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).

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

z² - 10z + 21 = 0
(z - 3)(z - 7) = 0

For this expression to be true, the left side of the expression must equal zero. Therefore, either (z - 3) or (z - 7) must equal zero:

If (z - 3) = 0, z must equal 3
If (z - 7) = 0, z must equal 7

So the solution is that z = 3 or 7

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.

-4x + 8 > 7 + 9x
-4x > 7 + 9x - 8
-4x - 9x > 7 - 8
-13x > -1
x > \( \frac{-1}{-13} \)
x > \(\frac{1}{13}\)

An exterior angle of a triangle is equal to the sum of the two interior angles that are opposite:

d° = b° + c°

To find angle c, remember that the sum of the interior angles of a triangle is 180°:

180° = a° + b° + c°
c° = 180° - a° - b°
c° = 180° - 49° - 60° = 71°

So, d° = 60° + 71° = 131°

A shortcut to get this answer is to remember that angles around a line add up to 180°:

a° + d° = 180°
d° = 180° - a°
d° = 180° - 49° = 131°