Question

How to find value of k?

Answer 1

cos^2x-sin^2x-1/√x^2+1-1
cos2x-1/√x^2+1-1
cox^2x/√x^2+1-1
cosx^2x((√x^2+1)+1)/x^2
let us apply limit..where x tends to zero

there fore
√1+1=k
since it is given that f(x) is continuous at 0
therefore k=2