Triangle angles

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If triangle DEF points A, B, and C are taken on DE, DF, and EF respectively such that EC = AC and CF = BC. If angle D = 40 degrees then what does angle ACB equal (in degrees)?

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My other question is about solving a trangle problem that requires me calculate the angle ACB in the triangle...

ne help or suggestion will be greatly appreaciated

thanx in advance :wave:

Mark your equal angles (with x,y for example). From the big triangle you find that x+y=140 deg. Then from (ECF)=180 you can easily find that (ACB)=100 deg