Two hiking trails intersect at point , forming four angles. One of the angles measures . The angle adjacent to this angle that forms a straight line with it is labeled . What is the value of ?
At intersecting lines, a linear pair is two touching angles whose outside rays form a straight line. That straight line is the cue to add their measures to , then subtract the known angle. Don’t use the rule for vertical angles: those sit across the intersection, not beside each other.
Hints
- Hint 1
A linear pair consists of two angles that share a side while their other sides point in opposite directions. Do the outer rays of the labeled angles make a straight line?
- Hint 2
Angles that fill a straight line add to . Add and the known angle, then subtract the known angle to find what remains.
Step-by-step
Use the straight angle
Step 1Write the angle equation
No Desmos needed. The missing angle takes one subtraction. The angle and share a side, and their other sides point in opposite directions. They form a linear pair. Angles that fill a straight line add to , so:
- Step 2
Find the missing angle
Subtract from both sides:
Finish the subtraction:
The angle labeled measures . Choice B.