Thread: What am I doing wrong in solving?

I'm back

Alright, the answer should be -126 and 124. I am able to get 124 but not -126. Here is what I'm doing:

$\displaystyle (3-(x+1)^{2/3})/2 = -11$

$\displaystyle 3-(x+1)^{2/3} = -22$

$\displaystyle -(x+1)^2/3 = -25$

$\displaystyle (x+1)^{2/3} = 25$

$\displaystyle x+1 = 125$

$\displaystyle x = 124$

I'm only getting one answer. Where is the -126 coming from?

Is there a plus/minus from a root you are not taking?

You should be a little more careful with your steps there. You have two mistakes which cancel each other out (line 2 to 3, and then line 3 to 4). Treat the problem like this:

$\displaystyle ((x+1)^{1/3})^{2} = 25.$ What does that suggest?

Originally Posted by Kieth89

I'm back

Alright, the answer should be -126 and 124. I am able to get 124 but not -126. Here is what I'm doing:

$\displaystyle (3-(x+1)^{2/3})/2 = -11$

$\displaystyle 3-(x+1)^{2/3} = -22$

$\displaystyle -(x+1)^2/3 = -25$

$\displaystyle (x+1)^{2/3} = 25$

$\displaystyle x+1 = 125$

$\displaystyle x = 124$

I'm only getting one answer. Where is the -126 coming from?

Your second last line is wrong. It should be $\displaystyle x + 1 = \pm 125$ since you have taken the square root of both sides.

Oh, I see now. Those get me every single time. I really need to remember the + and - deal whenever I'm solving with even roots.. Thanks for the help

Originally Posted by Kieth89

I don't think so... it's not an even root.

*Ahem* What do you think the power 2/3 means? To undo this power and hence get x + 1 you have cubed and then square rooted.