Question

Find the derivatives of the following functions at the indicated points :

sin x at x = π/2

Answer 1

Derivative of a function f(x) at any real number a is given by –

{where h is a very small positive number}

∴ derivative of sin x at x = π/2 is given as –

∵ we can’t find the limit by direct substitution as it gives 0/0 (indeterminate form)

So we need to do few simplifications to evaluate the limit.

As we know that 1 – cos x = 2 sin²(x/2)

Dividing the numerator and denominator by 2 to get the form (sin x)/x to apply sandwich theorem, also multiplying h in numerator and denominator to get the required form.