# Integration : different answers from two methods [duplicate]

There seems to be no way to get these expressions from both the methods to match. I know the arbitrary constant could vary in different methods but even the strcture of both these expressions are not close to same.

I know there is no calculation error because I differentiated the final expressions in both the methods to get the starting integrand.

Please tell me why the expressions don't match then.

• What expressions might those be? – amd Aug 21 '16 at 17:16
• It just wouldn't let me post the image. I have made the edits now. – Arishta Aug 21 '16 at 17:21
• Would you let me know which step did I do wrong? – Arishta Aug 21 '16 at 17:25
• I retract my statement. Both are correct. They differ in their constant term. – Ian Miller Aug 21 '16 at 17:26
• Can ypu show me how? – Arishta Aug 21 '16 at 17:28

The two terms are equivalent :

$$\frac15\tan\left({\frac{x-\tan^{-1}\frac34}{2}}\right)=\frac{1}{5}\left(\frac{3\tan\frac{x}{2} -1}{3+\tan\frac{x}{2}}\right)=\frac15\left(\frac{3\tan\frac{x}{2} +9 -10}{3+\tan\frac{x}{2}}\right)$$ $$=\frac35 +\frac{-2}{\tan\frac{x}{2} +3}$$

• How does this answer my question? – Arishta Aug 21 '16 at 17:46
• @user362725 I think this will answer your question. – Aakash Kumar Aug 21 '16 at 17:51

It's hard to tell where you made an error if you don't show your working, your result, or even the problem you're trying to solve.

But that said, I do know a lot of people have trouble seeing "the constants of integration are just different" when it's not directly obvious. For example, they would have trouble recognizing that both solutions

$$\sin^2 x + C_1 \qquad \qquad -\cos^2 x + C_2$$

are the same solution, because they did not think to check beyond simply adding a number to the formal expression.

If you really think you have two equal results, consider it a new math problem to see if the two results are the same or different. e.g. do one of the following two things:

Solve for the constant $A$ in $\sin^2 x + A = -\cos^2 x$

to see that they really are equal, or

Find two values $a$ and $b$ so that $(\sin^2 a) - (-\cos^2 a) \neq (\sin^2 b) - (-\cos^2 b)$ have different values.

to see that they really aren't equal. (and so there really must be some mistake or oversight)

• Please see the edits now. I have shown the working in the image. I think I considered every possible manipulation I knew but nothing worked out. – Arishta Aug 21 '16 at 17:24