JEE Main20202 Sep 2020Evening ShiftMathematicsInverse Trigonometric FunctionsActual
If y = ∑ k = 1 6 k cos - 1 3 5 cos k x - 4 5 sin k x then d y d x at x = 0 is
Correct answer
91
Step-by-step solution
For, small values near 0 , i.e., x < < . . 1 y = ∑ k = 1 6 k cos - 1 cos k x · cos α - sin k x · sin α = ∑ k = 1 6 k cos - 1 cos k x + α = ∑ k = 1 6 k k x + α = ∑ k = 1 6 k 2 x + k α d y d x = ∑ k = 1 6 k 2 = 6 7 13 6 = 91