The value of the integral \({ }^{1} \int_{0}\left(x^{5}+6 x^{4}+5 x^{3}+4 x^{2}+3 x+1\right) e^{x-1} d x\) is equal to...... (a) 5 (b) \(5 \mathrm{e}\) (c) \(5 \mathrm{e}^{2}\) (d) \(5 \mathrm{e}^{4}\)

Short Answer

Expert verified
The value of the integral is 5.

Step by step solution

01

Apply integration by parts

To solve this integral, we will apply integration by parts with \(u = x^5 + 6x^4 + 5x^3 + 4x^2 + 3x + 1\) and \(dv = e^{x-1}dx\). To apply the integration by parts, we first need to find the derivatives and antiderivatives of \(u\) and \(v\): \[ du = (5x^4 + 24x^3 + 15x^2 + 8x + 3) dx \] \[ v = \int e^{x-1} dx = e^{x-1} \] Now, apply integration by parts formula: \[ \int u dv = uv - \int v du \] Plug in \(u\), \(v\), and \(du\), and compute the integral: \[ \begin{aligned} \int_0^1 \left(x^5 + 6x^4 + 5x^3 + 4x^2 + 3x + 1\right) e^{x-1} dx &= \left[(x^5 + 6x^4 + 5x^3 + 4x^2 + 3x + 1)e^{x-1}\right]_0^1 - \int_0^1 e^{x-1}(5x^4 + 24x^3 + 15x^2 + 8x + 3) dx \\ \end{aligned} \]
02

Compute the definite integral

Now, find the definite integral of the above expression: \[ \begin{aligned} \int_0^1 \left(x^5 + 6x^4 + 5x^3 + 4x^2 + 3x + 1\right) e^{x-1} dx &= (1^5 + 6\cdot 1^4 + 5 \cdot 1^3 + 4 \cdot 1^2 + 3 \cdot 1 + 1)e^{1-1} - (0^5 + 6 \cdot 0^4 + 5 \cdot 0^3 + 4 \cdot 0^2 + 3 \cdot 0 + 1)e^{0-1}\\ &\quad - \int_0^1 e^{x-1}(5x^4 + 24x^3 + 15x^2 + 8x + 3) dx \\ &= (20-1)e^0 - \int_0^1 e^{x-1}(5x^4 + 24x^3 + 15x^2 + 8x + 3) dx \\ &= 19 - \int_0^1 e^{x-1}(5x^4 + 24x^3 + 15x^2 + 8x + 3) dx \\ \end{aligned} \]
03

Observe the remaining integral and choose the correct answer

Observe the remaining integral term: \[ \int_0^1 e^{x-1}(5x^4 + 24x^3 + 15x^2 + 8x + 3) dx \] Since all powers of \(x\) are strictly positive and the exponential function \(e^{x-1}\) is always positive for \(0 \le x \le 1\), the remaining integral term will strictly positive. Thus, the value of \[ 19 - \int_0^1 e^{x-1}(5x^4 + 24x^3 + 15x^2 + 8x + 3) dx \] will be strictly less than 19. Out of the given options, only option (a) with the value of 5 satisfies this condition. The answer is therefore: \[ \int_0^1 \left(x^5 + 6x^4 + 5x^3 + 4x^2 + 3x + 1\right) e^{x-1} dx = \boxed{5} \]

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