Integral (1) fixed

Calculus Level 3

7 17 ( x 3 29 x 2 + 281 x 890 ) d x = ? \large \int_7^{17} \left(x^3-29x^2+281x-890 \right) dx = \ ?


The answer is 923.3333.

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2 solutions

Chew-Seong Cheong
Aug 17, 2017

I = 7 17 ( x 3 29 x 2 + 281 x 890 ) d x = 7 17 ( x 3 21 x 2 + 147 x + 343 8 x 2 + 134 x 547 ) d x = 7 17 ( ( x 7 ) 3 8 ( x 2 14 x + 49 ) + 22 x 154 1 ) d x = 7 17 ( ( x 7 ) 3 8 ( x 7 ) 2 + 22 ( x 7 ) 1 ) d x Let u = x 7 = 0 10 ( u 3 8 u 2 + 22 u 1 ) d u = u 4 4 8 u 3 3 + 11 u u 0 10 = 2770 3 923.333 \begin{aligned} I & = \int_7^{17} \left(x^3-29x^2+281x-890 \right) dx \\ & = \int_7^{17} \left(x^3-21x^2+147x+343-8x^2+134x-547 \right) dx \\ & = \int_7^{17} \left((x-7)^3-8(x^2-14x+49) + 22x-154-1 \right) dx \\ & = \int_7^{17} \left((x-7)^3-8(x-7)^2+22(x-7)-1 \right) dx & \small \color{#3D99F6} \text{Let }u = x-7 \\ & = \int_0^{10} \left(u^3-8u^2+22u-1 \right) du \\ & = \frac {u^4}4 - \frac {8u^3}3 + 11u - u \bigg|_0^{10} \\ & = \frac {2770}3 \approx \boxed{923.333} \end{aligned}

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Aug 17, 2017

x 3 29 x 2 + 281 x 890 = ( x 10 ) 3 + ( x 10 ) 2 + ( x 10 ) x^3-29x^2+281x-890=(x-10)^3+(x-10)^2+(x-10) \ Now sub u = x 10 u=x-10 and we integrate from -7 to 7 So cubic and linear vanish becomes ( x 10 ) 3 3 \frac{(x-10)^3}{3} from -7 to 7 686 3 \boxed{\frac{686}{3}}

This was if lower bound was 3...

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