I had some problems trying to find the second derivative of some equations.

1. sec(x). I used the product rule when i got to the first deriv. but my answer came as sec x^3 which is incorrect and it says: sec(x)^3+secx*tanx^2 as the right answer.

2. e^x*cos x. Again I used the product rule and i got -e^x*cos x+e^x*cos x which is wrong and it says -2e^x*sin x is the right answer.

3.(sqrt x) I had a problem with the distribution and exponents. Anyways, I got x^1/2*(1/x)+(1/2 x^-1/2)*ln x. the right answer is -1/4*x^-3/2 *ln t.

Please help.