text: (sinx+cosx)squared = 2\n(sinx)squared + 2sinxcosx + (cosx)squared = 2 \n[since (a+b)squared = (a)squared +2ab + (b)squared ]\n\nnow u know that (sinx)squared  + (cosx)squared = 1\ntherefore the above equation becomes \n1 + 2sinxcosx = 2\ni.e. 2sinxcosx = 1\ni.e. sin2x =1 (since sin2x = 2sinxcosx )\nnow we know that sin (90) degree = 1\ntherefore here 2x = 90 degree\ni.e x = 45 degree\ni.e Cos x = Cos 45 = 1/Sqrt(2)