Inte(grity)

Level 2

Find the value of the integral:

6 x 4 5 x 3 + 4 x 2 2 x 2 x + 1 \large{\int\dfrac{6x^{4}-5x^{3}+4x^{2}}{2x^{2}-x+1}}

If the value can be expressed as:

a 1 . x 3 x 2 a 2 + 1 a 3 . l n ( a 4 x 2 x + 1 ) + 1 a 5 a 6 . t a n 1 ( a 7 x 1 a 8 ) + C \large{a_{1}.x^{3}-\dfrac{x^{2}}{a_2}+\dfrac{1}{a_3}.ln(|a_{4}x^{2}-x+1|)+\dfrac{1}{a_{5}\sqrt{a_6}}.tan^{-1}(\dfrac{a_{7}x-1}{\sqrt{a_8}})+C} ...... where C is the constant of integration \text{where C is the constant of integration}

Find the value of i = 1 8 a i \sum\limits_{i=1}^{8}{a_i}


The answer is 29.

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1 solution

Aritra Jana
Dec 22, 2014

We have:

6 x 4 5 x 3 + 4 x 2 2 x 2 x + 1 d x \large{\int\dfrac{6x^{4}-5x^{3}+4x^{2}}{2x^{2}-x+1}dx}

= x 2 ( 3 ( 2 x 2 x + 1 ) 2 x + 1 ) 2 x 2 x + 1 d x =\large{\int\dfrac{x^{2}(3(2x^{2}-x+1)-2x+1)}{2x^{2}-x+1}dx}

= 3 x 2 d x x ( 2 x 2 x + 1 1 ) 2 x 2 x + 1 d x =\large{\int 3x^{2}dx-\int\dfrac{x(2x^{2}-x+1-1)}{2x^{2}-x+1}dx}

= 3 x 2 d x x d x + 1 4 4 x 1 + 1 2 x 2 x + 1 d x =\large{\int 3x^{2}dx-\int xdx +\frac{1}{4}\int\dfrac{4x-1+1}{2x^{2}-x+1}dx}

= 3 x 2 d x x d x + 1 4 [ 4 x 1 2 x 2 x + 1 d x + 2 ( 2 x 1 2 ) 2 + ( 7 2 ) 2 d x ] =\large{\int 3x^{2}dx -\int xdx +\frac{1}{4}[\int\dfrac{4x-1}{2x^{2}-x+1}dx+\int\dfrac{2}{(2x-\frac{1}{2})^{2}+(\frac{\sqrt{7}}{2})^{2}}dx]}

Now:

4 x 1 2 x 2 x + 1 d x = d ( 2 x 2 x + 1 ) 2 x 2 x + 1 = l n ( 2 x 2 x + 1 ) \large{\int\dfrac{4x-1}{2x^{2}-x+1}dx=\int\dfrac{d(2x^{2}-x+1)}{2x^{2}-x+1}=ln(|2x^{2}-x+1|)}

also,

2 ( 2 x 1 2 ) 2 + ( 7 2 ) 2 d x = d ( 2 x 1 2 ) ( 2 x 1 2 ) 2 + ( 7 2 ) 2 = 2 7 t a n 1 4 x 1 7 \large{\int\dfrac{2}{(2x-\frac{1}{2})^{2}+(\frac{\sqrt{7}}{2})^{2}}dx=\int\dfrac{d(2x-\frac{1}{2})}{(2x-\frac{1}{2})^{2}+(\frac{\sqrt{7}}{2})^{2}}=\frac{2}{\sqrt{7}}tan^{-1}\dfrac{4x-1}{\sqrt{7}}}

we get \therefore \text{ we get } 1. x 3 x 2 2 + 1 4 l n ( 2 x 2 x + 1 ) + 1 2 7 t a n 1 4 x 1 7 \large{1.x^{3}-\frac{x^{2}}{2}+\frac{1}{4}ln(|2x^{2}-x+1|)+\frac{1}{2\sqrt{7}}tan^{-1}\dfrac{4x-1}{\sqrt{7}}}

comparing, we get:

a 1 = 1 ; a 2 = 2 ; a 3 = 4 ; a 4 = 2 ; a 5 = 2 ; a 6 = 7 ; a 7 = 4 ; a 8 = 7 a_1=1;a_2=2;a_3=4;a_4=2;a_5=2;a_6=7;a_7=4;a_8=7

our sum: 29 \boxed{29}

Good solution! It is on level 1 because at this stage you don't have much amount of followers. I am Resharing it so that it may get to some level!!

Ps:laborious one!

Parth Lohomi - 6 years, 5 months ago

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yes... only requires hard work to solve this :/

still, i found it worth sharing because of the complications..

Aritra Jana - 6 years, 5 months ago

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You shall post problems on definite integration

Parth Lohomi - 6 years, 5 months ago

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@Parth Lohomi yes i shall do so ..

Aritra Jana - 6 years, 5 months ago

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