Q. 4 A3.9( 50 Votes )
ABCD is a parallelogram. The ratio of ∠A and ∠B of this parallelogram is 5 : 4. Find the measure of ∠B.
Answer :
Given: ∠A : ∠B = 5:4
Let the measure of ∠A = 5x
Then ∠B = 4x
Since the adjacent angles of a parallelogram are complementary, therefore ∠A + ∠B = 180°
⇒ 5x + 4x = 180°
⇒ 9x = 180°
⇒ x = 20°
∴ ∠ A = 5x = 5 × 20° = 100°
∴ ∠ B = 4x = 4 × 20° = 80°
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