- #1
KLscilevothma
- 322
- 0
Here's the question that I got stuck:
[inte]sqrt[x/(a-x)] dx .........(*)
I tried to use the following substitution
u=sqrt[x/(a-x)] and ........(1)
dx = 2u(1-a)/(1+u2)2 du...(2)
sub (1) and (2) into (*), after a few steps, I got
(2-2a)[inte]du/(1+u2) - 2(1-a)[inte]du/(u2+1)2
The answer derived from the first part, (2-2a)[inte]du/(1+u2), contains tan -1 but the model answer of this question is
-[squ](ax-x2) + a/2sin-1[(2x+a)/a] + C
For the second part, I let u = tan θ and got a strange expression.
Is my approach correct and is the final answer obtained from the above method differs the model answer only by the constant of integration ? Or am I using a wrong substitution?
[inte]sqrt[x/(a-x)] dx .........(*)
I tried to use the following substitution
u=sqrt[x/(a-x)] and ........(1)
dx = 2u(1-a)/(1+u2)2 du...(2)
sub (1) and (2) into (*), after a few steps, I got
(2-2a)[inte]du/(1+u2) - 2(1-a)[inte]du/(u2+1)2
The answer derived from the first part, (2-2a)[inte]du/(1+u2), contains tan -1 but the model answer of this question is
-[squ](ax-x2) + a/2sin-1[(2x+a)/a] + C
For the second part, I let u = tan θ and got a strange expression.
Is my approach correct and is the final answer obtained from the above method differs the model answer only by the constant of integration ? Or am I using a wrong substitution?