prove

JEE Main 2015 Forum › Calculus questions › prove

prove that
2\pi <sin xx<1

for x e (0,\pi 2)

#Mathematics #Calculus

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6 Answers

11

Tush Watts ·2009-11-20 21:30:42

Ans) Let f(x) = sinxx
Since f(x) is dec in the interval (0 , âˆ©/2)

Therefore, f(0) > f(x) > f (âˆ©/2)
That implies, 1 > sinxx > 1âˆ©/2 = 2 / âˆ©

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1

Kaustab Sarkar ·2009-11-20 22:53:00

ths toh i know

but how to prove that f'(X)<0 for proving it to be dec func

how to prove that (xcosx-sinx)/x² is <0

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24

eureka123 ·2009-11-20 23:37:02

x²>0 for x>0
so only thing left to prove is xcosx-sinx<0

which is true iff sinx>xcosx
=> tanx>x

which is true ...(See graph)

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11

Devil ·2009-11-20 23:55:42

derivative of tanx is sec²x, which is â‰¥1.

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1

Kaustab Sarkar ·2009-11-21 00:23:57

ok thanq everyone... i got it :)

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Kaustab Sarkar ·2009-11-21 00:26:30

one more

prove taht f(x)=(1+1x)^1/x is monotonically increasing in its domain

and draw its graph also :)

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Your Answer

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