# Nspire CAS spitting out a wrong answer?

Consider the integral: $$\int \frac{8x+11}{(2x+3)(x+1)}$$ My Nspire CAS tells me that the answer to this is $$\ln\left\lvert(x+1)^3 \cdot (2x+3)\right\lvert$$

This is not the correct answer according to my calculations and Wolfram Alpha

Any ideas what's going on?

• Absolute value is ridiculous in LaTeX. It's \lvert expression \rvert. Of course, you could do any number of things, but purists always prefer this method. Nov 29, 2013 at 9:58
• Wolfram alpha tells you the same - if you check the footer, it defines log as the natural logarithm, i.e. ln. (Still a funny way to write it) Then: 3log(x+1) + log(2x+3) = log((x+1)^3) + log(2x+3) = log((x+1)^3(2x+3) Nov 29, 2013 at 12:57

HINT:

$$\frac{8x+11}{(2x+3)(x+1)}=\frac A{2x+3}+\frac B{x+1}$$

Do you know $\displaystyle \ln a+\ln b=\ln ab$ and consequently $\displaystyle c\cdot\ln a=\ln (a^c)$ (assuming if each logarithm is defined) ?

• Yes, I see that now. Thank you.
– Paze
Nov 29, 2013 at 9:59
• Hear, hear! Calculators, boo! Nov 29, 2013 at 9:59

$$\log ((x+1)^3 (2x+3)) = 3\log(x+1) + \log(2x+3)$$