Here is the problem:
3z^2 + 12z + 5 = 0 So there is this thing called the quadratic formula that I KNOW you know. I am perplexed as to why you are stuck. Or were you told to solve this particular problem by completing the square? Unless you tell us what the problem requires, our advice is likely to be unhelpful.
What I have..
3z^2 +12z = -5
If you are trying to "complete the square," Loren explained that it is very helpful to divide through by the coefficient of the squared term AS YOUR VERY FIRST STEP, and transposing the constant to the other side of the equation is no help at all AT THIS STAGE. So this is all OK mechanically, but it is not going anywhere helpful.
(3z^2 + 12z +9) = -5 + 9 Still good mechanically but still going nowhere rewarding.
(3z - 3) (z - 3) = (-14)^2
First of all, unless z = 0, 3z[sup:jxovuvc3]2[/sup:jxovuvc3] + 12z + 9 \(\displaystyle \neq\) (3z - 3)(z - 3) = 3z[sup:jxovuvc3]2[/sup:jxovuvc3] - 12z + 9. Second, if you had properly factored the left side of the equation, you would not have changed it so what justification is there for squaring the right side of the equation. Third, - 5 + 9 \(\displaystyle \neq\) - 14.
Aren't I supposed to be able to solve for z? Thanks.
