# Trapezium internal angles

A trapezium where AB is parallel to CD, has angle A : angle D = 4 :5, angle B = 3x-15 and angle C = 4x+20. Find angle A, B, C and D.

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**Partho**

Let Angle A=4x, B= 3x-15, C=4x+20 and D=5x.

Using the property that sum of adjacent angles = 180 we get:

A + D = 180 or 4x+5x=180.

Solving we get x=20.

Substituting we get: A=80, B=100

Similarly, B+C=180 or

3x-15+4x+20=180

Solving we get x=25

Substituting we get: B=60, D=120.

Using the property that sum of adjacent angles = 180 we get:

A + D = 180 or 4x+5x=180.

Solving we get x=20.

Substituting we get: A=80, B=100

Similarly, B+C=180 or

3x-15+4x+20=180

Solving we get x=25

Substituting we get: B=60, D=120.

#### To solve this example are needed these knowledge from mathematics:

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