# Thread: Algebra- what went wrong?

1. ## Algebra- what went wrong?

Ok I had to find the derivitive of some ugly equation, and I started simplifying till I got to this point:

If I substitute t for 2, then I get an answer of about 34, which is the answer I need, however, when I continued to simplify:

But when I sub 2 for t now, my answer is 74? Where did I go wrong in my simplifying.

2. Originally Posted by iphysics
Ok I had to find the derivitive of some ugly equation, and I started simplifying till I got to this point:

If I substitute t for 2, then I get an answer of about 34, which is the answer I need, however, when I continued to simplify:

But when I sub 2 for t now, my answer is 74? Where did I go wrong in my simplifying.
For the numerator:
$\displaystyle -ln(t/4+1)*2t(t+4)~~~~~=~~~~~ -ln(t/4+1)*2t^2 -ln(t/4+1)*8t$

For the denominator:
I'm not sure what you were shooting for, but $\displaystyle \frac{t+4}{(t^2+25)^2}$ does not equal $\displaystyle (t+4)(t^2+25)^2$

for example, a=t+4, b=(t^2+25)^2

Then you have the denominator as a divided by b equals a times b. Since division and multiplication are not the same thing, this is not true.

3. Nevermind I got it!!