Answer:
a. (A, B, C) = (90°, 65°, 25°)
b. BCD = 155°
Step-by-step explanation:
The interior acute angles of the right triangle can be found by writing an equation representing the relation between them. The exterior angle can be found using the relations between exterior angles and interior angles.
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a.
Angle A is given as a right angle, so measures 90°. Let C represent the measure of angle C in degrees. Then angle B has measure 3C-10. Those two angles are complementary, so ...
C +(3C-10) = 90
4C = 100
C = 25
B = 3(25) -10 = 65
The angle measures are ...
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b.
Angle BCD is the exterior angle adjacent to interior angle C. As such, it is supplementary to angle C:
BCD = 180° -C = 180° -25° = 155°
An exterior angle is equal to the sum of the remote interior angles. That means ...
BCD = A +B = 90° +65° = 155°
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Additional comment
An exterior angle is equal to the sum of the remote interior angles, because both the exterior angle and the sum of the remote interior angles are supplementary to the adjacent interior angle. Angles supplementary to the same angle have the same measure.