# In a triangle ABC, the angle is C = 90, AB = 12. The outside angle at apex B is 120. Find BC.

January 13, 2021 | education

| If the angle is C = 90, then it is a right-angled triangle.

Find angle B:

Angle B = 180 – 120 = 60;

Find angle A:

angle A = 90 – 60 = 30;

In a right-angled triangle, a leg opposite an acute angle of 30 ° is half the hypotenuse.

Means:

BC = AB / 2 = 12/2 = 6;

Answer: BC = 6

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