# Thread: Final in 2 hours, Zeros, amplitude, period etc

1. ## 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?

2. Originally Posted by Garface
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?
Hi

1. 0,-7,3 are the zeros of $\displaystyle x^3 + 4x^2-21x$ but you have also to find the zeros of $\displaystyle x^2 + 2x - 7$

2. OK since $\displaystyle x^4 + 6x^2 + 9 = (x^2+3)^2$

3. OK

3. For number one I didnt think there were any real zeros of the left hand side of the equation or at least not any that i could find. Graphing it I noticed that the parabola did cross the x axis but i tried using those numbers and it did not come out to exact zeros.

4. Have you tried the quadratic equation?

$\displaystyle x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}$

For a quadratic of the form:

$\displaystyle ax^2+bx+c$