Question

Q) If A +B+C = 180 and cos A = cos B cos C. then tan B tan C is equal to. a) 1/2
b) 2
c) 1
d) -1/2​

Answer 1

Answer:

A + B + C = 180

A = 180 - (B+C)

cos A = cos B. cos C      then subtitute A

cos (180-(B+C)) = cos B. cos C

-cos(B+C) = cos B. cos C        

-(cos B. cos C - sin B sin C) = cos B. cos C

-cos B. cos C + sin B sin C = cos B. cos C

sin B sin C = 2  cos B. cos C

(sin B sin C) /  (cos B. cos C) =2

tan B tan C = 2

Step-by-step explanation:

Rules

1 . Cos (A+B) = Cos A Cos B - Sin A Sin B