Q13 of 31 Page 316

If sin 10θ = cos8θ and 10θ is a positive acute angle, let us find the value of tan 9θ.

Given, sin10θ = cos8θ


And 10θ is a positive acute angle


⇒ sin10θ = cos8θ


⇒ cos(90 - 10θ) = cos8θ


⇒ 90 - 10θ = 8θ


⇒ 90 = 18θ


⇒ θ = 5


Hence, the value of θ is 5


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