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how to do intergration of $${\frac{{\mathtt{2}}{\mathtt{\,\times\,}}{\mathtt{x}}}{\left({{\mathtt{x}}}^{{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{1}}\right)}}$$

 Sep 29, 2014

Best Answer 

 #5
avatar+33661 
+13

Both product and quotient rule are for differentiating a product.  It just happens that the "product" involves a factor in the denominator when using the quotient rule.

In fact, I never bother trying to remember the quotient rule.  I just use the product rule combined with the chain rule to differentiate a quotient.  So, for example I would differentiate y = u/v as follows

y = u*v-1

dy/dx = u*d(v-1)/dx + v-1*du/dx

dy/dx = u*d(v-1)/dv*dv/dx + v-1*du/dx

dy/dx = -(uv-2)*dv/dx + v-1*du/dx

dy/dx = -(u/v2)*dv/dx +(1/v)*du/dx

 

Of course this can be rearranged to look like the standard quotient formula, but I find it easier just to apply the steps above directly to the specific functions involved!

 Sep 29, 2014
 #1
avatar+1313 
+3

wrong and removed

 Sep 29, 2014
 #2
avatar+33661 
+13

It can be done more simply Stu.

 

Let y = x2 + 1

Then dy = 2xdx

 

∫2x/(x2+1)dx = ∫dy/y = ln(y) = ln(x2 + 1)  (plus an arbitrary constant of integration of course).

 Sep 29, 2014
 #3
avatar+1313 
+3

Alan would it be a product rule or quotient rule? One is for integral and one for derivatives, opposites to each other?

 Sep 29, 2014
 #4
avatar+1313 
+3

i was going to go with substitution method haha, i still get confused by making the term dy but a little ok i guess. would the product rule have worked or not worked?

 Sep 29, 2014
 #5
avatar+33661 
+13
Best Answer

Both product and quotient rule are for differentiating a product.  It just happens that the "product" involves a factor in the denominator when using the quotient rule.

In fact, I never bother trying to remember the quotient rule.  I just use the product rule combined with the chain rule to differentiate a quotient.  So, for example I would differentiate y = u/v as follows

y = u*v-1

dy/dx = u*d(v-1)/dx + v-1*du/dx

dy/dx = u*d(v-1)/dv*dv/dx + v-1*du/dx

dy/dx = -(uv-2)*dv/dx + v-1*du/dx

dy/dx = -(u/v2)*dv/dx +(1/v)*du/dx

 

Of course this can be rearranged to look like the standard quotient formula, but I find it easier just to apply the steps above directly to the specific functions involved!

Alan Sep 29, 2014
 #6
avatar+1313 
+3

but they cannot solve for integal?

 Sep 29, 2014
 #7
avatar+33661 
+3

In the case of the integral you use the product form the other way round

 

Starting with  d(u*v)/dx = u*dv/dx + v*du/dx

Rewrite as  u*dv/dx = d((u*v)/dx - v*du/dx

 

Integrate each term 

∫udv = u*v - ∫vdu

 Sep 29, 2014
 #8
avatar+1313 
+3

i saw that on the formulas and thanks.

 Sep 29, 2014
 #9
avatar+118673 
+8

Stu and Archy

 

$$\int \frac{f'(x)}{f(x)}dx=ln[f(x)]+c$$

 

This is an integral that you need to automatically recognise!

 Sep 29, 2014

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