Question

a(b cos C-c cos B) =b2-c2 of subject math of class 12

Answer 1

law of cosines:

c² = a² + b² - 2ab cos y

converting equation in law of cosines

b^2 = a^2 + c^2 - 2ac cos B
c^2 = a^2 + b^2 - 2ab cos C

Second equation is subtracted from the first one
and the result came

b^2 - c^2 = c^2 - b^2 - 2ac cos B + 2ab cos C

c^2  and - b^2 goes on the other side of the = gives

2b^2 - 2c^2 = -2ac cos B + 2ab cos C

c^2 - b^2 come in brackets and 2 is taken as common gives

 2(b^2 - c^2) = 2a(-c cos B + b cos C)

So b^2 - c^2 = a(b cos C - c cos B)


MARK BRAINLIEST....