# The ABC triangle is isosceles. the angle ABC is equal to 20 degrees through the vertex B of this triangle

July 28, 2021 | education

| **The ABC triangle is isosceles. the angle ABC is equal to 20 degrees through the vertex B of this triangle a straight line EF is drawn parallel to the straight line AC, find 1) angle ABE 2) angle CBF 3) angle BAC and CB**

Since the triangle ABC is isosceles, its angles at the base of the AC are equal.

Angle BAC = BCA = (180 – ABC) / 2 = (180 – 20) / 2 = 80.

According to the condition, the straight line EF is parallel to AC, then the angle ABE = BAC = 80, as the angles lying crosswise at the intersection of parallel straight lines EF and AC secant AC.

Similarly, the angle CBF = BCA = 80.

Answer: 1) Angle ABC = 80, 2) angle CBF = 800, 3) angle BAC = BCA = 80.

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