16Hit1600
Geometry and TrigonometryVery hardAngle between a bisector and a side

Geometry and Trigonometry practice question

In triangle RST, RS = RT and angle S measures 36°. The bisector of angle R meets ST at U. What is the measure, in degrees, of angle RUS?

Answer: 90

Angle R is 108°, its bisector makes angle SRU 54°, and in triangle RSU the third angle is 180 − 36 − 54 = 90.

Common wrong answers

If you answered 54
54 is angle SRU.
If you answered 72
72 is angle T's supplement of 108, not angle RUS.
If you answered 108
108 is angle R.

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