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Maximising integrals

Suppose \(a<b\). Then find maximum value of the integral

\(\displaystyle \int_a^b (\frac{3}{4} - x - x^2) dx\) over all possible values of \(a,b\).

Note by Paramjit Singh
3 years, 5 months ago

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{a}^{b}((3/4)-x-x²)dx=(d/(da)) ((1/3)a³+(1/2)a²-(3/4)a-(1/3)b³-(1/2)b²+(3/4)b)= a²+a-(3/4)=0, Solution is: (1/2),-(3/2) (d/(db)) ((1/3)a³+(1/2)a²-(3/4)a-(1/3)b³-(1/2)b²+(3/4)b)= -b²-b+(3/4)=0, Solution is: (1/2),-(3/2) ∫{-(3/2)}^{(1/2)}((3/4)-x-x²)dx= 1. 3333 Carlos Suarez · 3 years, 2 months ago

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Answer=1.3333333 Carlos Suarez · 3 years, 2 months ago

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Sketch a graph and it becomes clear what are the values of a and b. Note that a definite integral is the area under the curve. Pranav Arora · 3 years, 5 months ago

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Hint : The integrand is positive only between two values that are its roots, take them as a and b to maximise the integral. Jatin Yadav · 3 years, 5 months ago

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@Jatin Yadav Find the area, my friend, I know how to do this. Find the answer. Never mind, thanks. Paramjit Singh · 3 years, 5 months ago

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