Question 863469
What do you mean "able to do f(x)"?
Substitute {{{pi/2}}} for {{{x}}}.
{{{f(pi/2)=2cos^2(pi/2)+sin(pi/2)- 1}}}
 {{{f(pi/2)=2(0)^2+1- 1}}}
  {{{f(pi/2)=0+1-1}}}
 {{{f(pi/2)=0}}}