Evaluating Integral

q_fruit

New member
Joined
Jun 13, 2005
Messages
28
Using u-substitution I tried evaluating the integral (3-2s)^1/2 x ds and I was so sure of my answer, but I keep getting it wrong. Please help! Thanks.
 
Show what you have tried, so we can see where you went wrong.
 
let u = 3-2s
du= -2ds
-1/2du = ds

(sorry im not familiar with TeX so i'll just use * to represent the integral sign)

*(3-2s)^1/2ds
= *u^1/2 x 1/2du
= -1/2 * u^1/2du
= -1/2 x (2/3)(u^3/2) + C
= -1/2 x (2/3)([3-2s]^3/2) + C
= -(2/6)(3-2s)^3/2 + C
 
Looks great, q_fruit! Perhaps they just wrote it differently?

\(\displaystyle \L -\frac{1}{3}(3 - 2s)^{\frac{3}{2}} \, + \, C\)

or

\(\displaystyle \L -\frac{1}{3}\sqrt{(3 - 2s)^3 \, } \, + \, C\)

or

\(\displaystyle \L -\frac{(3 - 2s)^{\frac{3}{2}}}{3} \, + \, C\)


or

\(\displaystyle \L -\frac{\sqrt{(3 - 2s)^3 \, }}{3} \, + \, C\)

That's me out of ideas.
 
Well, then, if we work backwards and differentiate that we get
\(\displaystyle \L (5s + 4)^{-\frac{1}{2}} = \frac{1}{\sqrt{5s + 4}}\)

Are you sure you're looking at the right answer?
 
I just realized the answer to #11 to the textbook is actually the answer to #13 and vice versa, hah..an error in the txtbook..*sigh* sorry for wasting your time!
 
Top