# Thread: Not sure I'm doing this the right way

1. ## Not sure I'm doing this the right way

I need to solve this in terms of x

3y(3y-x) = 2z(x+2z)

9y2 - 3yx = 2zx + 4z2

9y2 - 4z2 = 3yx + 2zx

(9y - 4z)(9y + 4z) = x(2z + 3y)

x = (9y - 4z)(9y + 4z) / (2z + 3y)

don't know if I can cancel to give this

x = (3y - 2z)(3y + 2z)

x = 9y2 + 3y2z - 3y2z - 4b2

x = 9y2 - 4b2

Really don't know if I've done this properly. Can anyone help?

Thanks.

2. ## Re: Not sure I'm doing this the right way

Originally Posted by kx110
I need to solve this in terms of x

3y(3y-x) = 2z(x+2z)

9y2 - 3yx = 2zx + 4z2

9y2 - 4z2 = 3yx + 2zx

(9y - 4z)(9y + 4z) = x(2z + 3y)

x = (9y - 4z)(9y + 4z) / (2z + 3y)
this is as far as you can go ...

3. ## Re: Not sure I'm doing this the right way

I thought it might be, I was just guessing with the rest. Do you think it's necessary to convert 9y2 - 4z2 to (9y - 4z)(9y + 4z) or is that over complicating it?

Thanks for your help.

4. ## Re: Not sure I'm doing this the right way

Originally Posted by kx110
I thought it might be, I was just guessing with the rest. Do you think it's necessary to convert 9y2 - 4z2 to (9y - 4z)(9y + 4z) or is that over complicating it?

Thanks for your help.
it's a matter of choice ... I prefer to have it factored in case one has to find zeros of the expression, etc.