Question

in parallelogram ABCD A=1/3angleB find out the angels

Answer 1

Angle a + angle b = 180 (they form supplementary angles)
100 + angle b = 180
angle b = 180 - 100 = 80°

angle a = angle c = 100°   (opposite angles of a parallelogram are equal)
angle b = angle d = 80°     (opposite angles of a parallelogram are equal)
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