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By using the properties of the definite integral, evaluate the integral: ∫0π2cos2xdx

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प्रश्न

By using the properties of the definite integral, evaluate the integral:

`int_0^(pi/2) cos^2 x dx`

योग
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उत्तर

Let `I = int_0^(pi/2) cos^2 x  dx`           ....(i)

and `I = int_0^(pi/2) cos^2 (pi/2 - x)  dx`

`= int_0^(pi/2)  sin^2 x  dx`          ....(ii) `[∵ int_0^a f (x) dx = int_0^a f (a - x) dx]`

Adding (i) and (ii), we get

`2 I = int_0^(pi/2) cos^2 x  dx + int_0^(pi/2) sin^2 x dx`

`= int_0^(pi/2) (sin^2 x + cos^2 x) dx`

`= int_0^(pi/2) dx = [x]_0^(pi/2)`

`= pi/2`

⇒ `I = pi/4.` 

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अध्याय 7: Integrals - Exercise 7.11 [पृष्ठ ३४७]

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एनसीईआरटी Mathematics Part 1 and 2 [English] Class 12
अध्याय 7 Integrals
Exercise 7.11 | Q 1 | पृष्ठ ३४७

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