Q. 26

# Prove that: <span

Answer : Proof:

Identities used: Therefore,

tan 15° = tan (45° - 30°)     On rationalising:  { (a – b)(a + b) = a2 – b2}      On rationalising  { (a – b)(a + b) = a2 – b2}  Let 2θ = 15° We know,    Formula used:   { (a + b)2 = a2 + b2 + 2ab}  cot θ < 0 as θ is in 1st quadrant.

So,  { (a + b)2 = a2 + b2 + 2ab}      { cot θ = tan(90° - θ)} Hence Proved

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