3x Integral

Calculus Level 5

A = 0 1 2 x 3 cos ( x 2 ) x + 4 5 y + 5 y 2 + y 2 y \mathbb{A} = \int_{0}^{1} 2x^3 \cos(x^2) \partial x + \int_{4}^{5} \dfrac{y+5}{y^2+y-2} \: \partial y

The above definite integral A \mathbb{A} has a real value of log ( a b ) + sin ( c ) + cos ( d ) + f \log\left ( \dfrac{a}{b} \right ) + \sin(c) + \cos(d) + f , where a , b , c , d , f a,b,c,d,f are integers and the fraction a b \dfrac{a}{b} is of simplest form.

Evaluate b a 6 ( c z 2 + d z + f ) z \displaystyle \int_{b}^{a} 6(cz^2+dz+f)\partial z .


The answer is 48697.

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1 solution

Guilherme Niedu
Feb 13, 2017

= 0 1 2 x 3 c o s ( x 2 ) d x + 4 5 y + 5 y 2 + y 2 d y \large = \int_0^1 2x^3 cos(x^2)dx + \int_4^5 \frac{y+5}{y^2+y-2}dy

x 2 = u \color{#3D99F6} x^2 = u

2 x d x = d u \color{#3D99F6} 2xdx = du

= 0 1 u c o s ( u ) d u + 4 5 ( 2 y 1 1 y + 2 ) d y \large = \int_0^1 ucos(u)du + \int_4^5 ( \frac{2}{y-1} - \frac{1}{y+2} ) dy

= u s i n ( u ) 0 1 0 1 c o s ( u ) d u + 2 l n ( y 1 ) 4 5 l n ( y + 2 ) 4 5 \large = usin(u) \Big |_0^1 - \int_0^1 cos(u)du + 2ln(y-1) \Big |_4^5 - ln(y+2) \Big |_4^5

= s i n ( 1 ) + c o s ( u ) 0 1 + 2 l n ( 4 3 ) l n ( 7 6 ) \large = sin(1) + cos(u) \Big |_0^1 + 2ln(\frac43) - ln(\frac76)

= s i n ( 1 ) + c o s ( 1 ) 1 + l n ( 4 3 2 6 7 ) \large = sin(1) + cos(1) - 1 + ln(\frac43 ^2 \cdot \frac67)

= l n ( 32 21 ) + s i n ( 1 ) + c o s ( 1 ) 1 \large = ln(\frac{32}{21}) + sin(1) + cos(1) - 1

So a = 32 , b = 21 , c = d = 1 , f = 1 \color{#D61F06} a=32, b=21, c=d=1, f=-1

Then:

21 32 ( 6 z 2 + 6 z 6 ) d z \large \int_{21}^{32} (6z^2 + 6z - 6)dz

= 2 z 3 + 3 z 2 6 z 21 32 \large = 2z^3 + 3z^2 - 6z \Big |_{21}^{32}

= 48697 \large = \color{#3D99F6} \fbox{48697}

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