Angles $a$ and $b$ are supplementary. If angle $a$ has a measure of $80°$, what is the measure of angle $b$?

• A. $100°$
• B. $90°$
• C. $80°$
• D. $180°$

Answer: (A)

Verified step by step guidance

1. Recall that supplementary angles are two angles whose measures add up to 180 degrees. This means that if angles a and b are supplementary, then their measures satisfy the equation \(a + b = 180^\circ\).
2. Identify the given information: angle a measures 80 degrees, so we can write \(a = 80^\circ\).
3. Substitute the known value of angle a into the supplementary angles equation: \(80^\circ + b = 180^\circ\).
4. To find the measure of angle b, isolate b by subtracting 80 degrees from both sides of the equation: \(b = 180^\circ - 80^\circ\).
5. Simplify the right side to express the measure of angle b in degrees, which completes the solution process.