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° - 70° = 72°

So, d° = 70° + 72° = 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°

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.

-5a - 1 < \( \frac{a}{5} \)
5 x (-5a - 1) < a
(5 x -5a) + (5 x -1) < a
-25a - 5 < a
-25a - 5 - a < 0
-25a - a < 5
-26a < 5
a < \( \frac{5}{-26} \)
a < -\(\frac{5}{26}\)

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.

5a + 4a = 9a

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

-c - 7y = -8c - 8y + 4
-c = -8c - 8y + 4 + 7y
-c + 8c = -8y + 4 + 7y
7c = -y + 4
c = \( \frac{-y + 4}{7} \)
c = \( \frac{-y}{7} \) + \( \frac{4}{7} \)
c = -\(\frac{1}{7}\)y + \(\frac{4}{7}\)

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°).