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° - 40° - 40° = 100°

So, d° = 40° + 100° = 140°

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° - 40° = 140°

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

sa = 2πr² + 2πrh
sa = 2π(9²) + 2π(9 x 1)
sa = 2π(81) + 2π(9)
sa = (2 x 81)π + (2 x 9)π
sa = 162π + 18π
sa = 180π

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).

A right angle measures 90 degrees and is the intersection of two perpendicular lines. In diagrams, a right angle is indicated by a small box completing a square with the perpendicular lines.

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.

6z - 4 < \( \frac{z}{-8} \)
-8 x (6z - 4) < z
(-8 x 6z) + (-8 x -4) < z
-48z + 32 < z
-48z + 32 - z < 0
-48z - z < -32
-49z < -32
z < \( \frac{-32}{-49} \)
z < \(\frac{32}{49}\)