Question

Differentiate cos x by abinitio or by first principal method.
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Answer 1

To find the derivative of sinx, we return to the first principles definition of the derivative of y=f(x): dydx=limh→0f(x+h)−f(x)h. dydx=limh→0sin(x+h)−sinxh. limh→0sin(x+h)−sinxh=limh→02cos(x+h2)sin(h2)h.