# Thread: Integral problem :(

1. ## Integral problem :(

Could someone solve this for me please?
I haven't got an idea how to solve this, therefore
please provide answer and show step-by-step would be really appreciated..
Thank you.

a) 2e^(7x)/e^(5x) dx

b)x^2 sqrt (7-3x^3) dx

c) x^3 sqrt ( x-3) dx

Thank you! I don't need an explanation, I'll try to find out by my self,
therefore please get me easy working + answer Thanks

2. Originally Posted by kunkka Could someone solve this for me please?
I haven't got an idea how to solve this, therefore
please provide answer and show step-by-step would be really appreciated..
Thank you.

a) 2e^(7x)/e^(5x) dx

b)x^2 sqrt (7-3x^3) dx

c) x^3 sqrt ( x-3) dx

Thank you! I don't need an explanation, I'll try to find out by my self,
therefore please get me easy working + answer Thanks
It's against the forum rules to completely give you the answer and working unless you've shown your working

a) $\displaystyle 2\dfrac{e^{7x}}{e^{5x}} = 2e^{7x-5x} = 2e^{2x}$

Use the rule: $\displaystyle \int e^{ax} = \dfrac{1}{a}e^{ax}$

b) This requires you to use integration by parts twice

Integration by parts: $\displaystyle \int u\,dv = uv - \int v\,du$

Let $\displaystyle u = x^2$ to get you started.

c) As above but use it three times

If you do not understand show how far you get

3. Just in case a picture helps for b)... ... where (key in spoiler) ...

Spoiler: ... is the chain rule. Straight continuous lines differentiate downwards (integrate up) with respect to the main variable (in this case x), and the straight dashed line similarly but with respect to the dashed balloon expression (the inner function of the composite which is subject to the chain rule).

The general drift is... Similarly, for c), using u = sqrt(x-3), i.e. x = u^2 + 3... Fill the blanks and continue the anti-clockwise journey towards the integral, I.

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4. Thanks alot for your help!!!!!!

5. Originally Posted by kunkka [snip]

b)x^2 sqrt (7-3x^3) dx

c) x^3 sqrt ( x-3) dx

Thank you! I don't need an explanation, I'll try to find out by my self,
therefore please get me easy working + answer Thanks
b) Substitute u = 7 - 3x^3.

c) Substitute u = x - 3. Then expand $\displaystyle (u+3)^3 u^{1/2}$ and integrate term-by-term.

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