In a △ABC, if 3∠A = 4 ∠B = 6∠C, then ∠A + ∠B - 3∠C =
(A) 70°
(B) 40°
(C) 20°
(D) 60°
confusing
Ans 1:
Class : Class 7
3 ∠A = 4 ∠B = 6 ∠CL.C.M. of 3, 4 and 6 = 12We know, ∠A ∠B ∠C =180°12 ∠A 12 ∠B 12 ∠C = 12 × 180°12 ∠A 3 (4 ∠B) 2 (6 ∠C) = 12 × 180°12 ∠A 3 (3 ∠A) 2 (3 ∠A) = 12 × 180°12 ∠A 9 ∠A 6 ∠A = 12 × 180°27 ∠A = 12 × 180°∠A = 12 × 180° / 27 = 80°∠B = 3⁄4 ∠A = 3⁄4 of 80° = 60°∠C = 3⁄6 ∠A = 1⁄2 of 80° = 40°Therefore, ∠A ∠B - 3 ∠C = 80° 60° - 3 × 40°= 140° - 120°= 20°Answer-(C) 20°