Calculus 5 - by Vlad Vasilescu (W)

Calculus Level 3

1 2 e m x 2 + ln x d x = 1 m \large \int_1^{\sqrt2} e^{mx^2 + \ln x} \ dx = \frac1m

Find the positive value of m m to 2 decimal places that satisfies the equation above.

Notation: e 2.71828 e \approx 2.71828 denotes the Euler's number .


The answer is 0.69.

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1 solution

Vlad Vasilescu
Dec 19, 2016

\int\limits_1^\sqrt{2} e^{m \cdot x^2 + ln(x)} dx = \int\limits_1^\sqrt{2} e^{m \cdot x^2} \cdot e^{ln(x)} dx = \int\limits_1^\sqrt{2} x e m x 2 d x = e m x 2 2 m 1 2 = e m ( e m 1 ) 2 m = 1 m x \cdot e^{m \cdot x^2} dx =\left. \frac {e^{m \cdot x^2}}{2 \cdot m} \right|_1^{\sqrt{2}} = \frac {e^m \cdot (e^m-1)}{2 \cdot m} = \frac {1}{m} . e m ( e m 1 ) = 2 \Rightarrow e^m \cdot (e^m-1) = 2 . We make the notation e m = t e^m = t and we get t 1 = 2 t_{1} = 2 and t 2 = 1 t_{2} = -1 .

  • for t = 2 t = 2 we get m = l n ( 2 ) m = ln(2)
  • for t = 1 t = -1 there are no solutions for m

Hence , our answer will be m = l n ( 2 ) 0.69 m = ln(2) \approx \boxed{0.69}

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