Here are a few problems I missed on the test. The professor doesn't show where you missed the problem or anything. Would like to know how to work these:

1) Solve for x: $\displaystyle tan(pi(x)/2)=0$

2) Solve for x: $\displaystyle 1-2cos(x)=0$

3) Calculate (give exact answers. i.e. no decimals)

a: $\displaystyle sin(105)$

b: $\displaystyle cos(7pi/12)$

4)Solve for x: $\displaystyle 2sin^2x=1+cos^2x$

Thanks for any help!