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° - 38° - 63° = 79°

So, d° = 63° + 79° = 142°

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° - 38° = 142°

An isosceles triangle has two sides of equal length. An equilateral triangle has three sides of equal length. In a right triangle, two sides meet at a right angle.

Parallel lines are lines that share the same slope (steepness) and therefore never intersect. A transversal occurs when a set of parallel lines are crossed by another line. All of the angles formed by a transversal are called interior angles and angles in the same position on different parallel lines equal each other (a° = w°, b° = x°, c° = z°, d° = y°) and are called corresponding angles. Alternate interior angles are equal (a° = z°, b° = y°, c° = w°, d° = x°) and all acute angles (a° = c° = w° = z°) and all obtuse angles (b° = d° = x° = y°) equal each other. Same-side interior angles are supplementary and add up to 180° (e.g. a° + d° = 180°, d° + c° = 180°).

To solve this equation, isolate the variable for which you are solving (a) on one side of the equation and put everything else on the other side.

-6a + 5x = -3a - 3x + 5
-6a = -3a - 3x + 5 - 5x
-6a + 3a = -3x + 5 - 5x
-3a = -8x + 5
a = \( \frac{-8x + 5}{-3} \)
a = \( \frac{-8x}{-3} \) + \( \frac{5}{-3} \)
a = 2\(\frac{2}{3}\)x - 1\(\frac{2}{3}\)

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

sa = 2πr² + 2πrh
sa = 2π(2²) + 2π(2 x 1)
sa = 2π(4) + 2π(2)
sa = (2 x 4)π + (2 x 2)π
sa = 8π + 4π
sa = 12π