We know cos 2x = 2cos²x – 1

Putting values in I we get,

Put cosx = t

Differentiating w.r.t to x we get,

sinx dx = -dt

Putting values in integral we get,

Again put √2× t = u

Differentiating w.r.t to t we get,

Putting values in integral we get,

Substituting value of u we get,

Substituting value of t we get,