Final in 2 hours, Zeros, amplitude, period etc

1. find the zeros of $\displaystyle (x^2 + 2x - 7) (x^3 + 4x^2-21x)$

I got 0,-7,3 was hoping someone could do it and see if they get the same answer.

2.$\displaystyle x^4 + 6x^2 + 9$

I got no real zeros

3. Find the amplitude, period and phase shift. $\displaystyle y = cos(2t + pi/2)$

I got: amplitude = 1, period = pi, phase shift = pi/2

Any help on any of them is EXTREMELY welcome. Thanks a million

*edit* just put this in the pre calc help area seeing as I think I will get replys quicker and then noticed in the rules not to double post and I dont want to be a pest there a delete button for the entire thread?