Explanation:
50°
abc is right angle and
a is 40°
b is 90°
c is 50°
so angle acb is vertical opposite to angle ecd and it is equal
total angles of the triangle = 180°
∠BAC + ∠ABC + ∠ACB = 180°
40° + 90° + ∠ACB = 180°
130° + ∠ACB = 180°
∠ACB = 180° - 130°
∠ACB = 50°
∠ACB and ∠ECD is opposite angles. So, that two angles are equal.
∠ACD = ∠ECD = 50° (B)
That's it :)
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