ZHENG YONG TAN's answer to help's Secondary 4 A Maths Singapore question.

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ZHENG YONG TAN
Zheng Yong Tan's answer
2 answers (Tutor Details)
1st
take note that I added a negative sign before and after the integration sign to the expression so the integration would be more straightforward

to do integration you have to be comfortable with your differentiation first, and then the integration will come to you much more easily.

do let me know in the comment if you still have any trouble. goodluck!
help
Help
2 years ago
where did -sinx go integrate -sinx dont you get cos x so isnt it -cosx/sinx e ^cos x
ZHENG YONG TAN
ZHENG YONG TAN
2 years ago
you can see that the expression that you are required to integrate is already in the form of f'(x)e^[f(x)].
- for the integration for f'(x)e^[f(x)], we simply get e^[f(x)] + C
- you can see that the differential of cosx is -sinx
- the expression is already somewhat in the form of f'(x)e^[f(x)], however you need to add a negative sign inside and outside of the integral to get the needed form
- then you can integrate to get -e^cos(x) + C

the -sinx is the f'(x) in f'(x)e^[f(x)], and so when you integrate it just becomes e^[f(x)] which is e^cos(x) +C
help
Help
2 years ago
i still dont get it if i integrate sinx e^cos x shouldnt i integrate sinx = -cosx and integrate e^cosx = 1/-sinx e^cosx so overall integrate sinx e^cos x = cosx/sinx e^cosx = tanx e^cosx
but then when i differentiate it back its wrong so im so confused