IIT JEE , AIEEE Forum - Mathematics , Differential Calculus

v_gurucharan

Q1 .
FIND THE INTERVALS IN WHICH f(x)= LOG(1+x)-X/1+X IS INCREASING OR DECREASING
Q2 .
FIND THE INTERVALS IN WHICH f(x)=SIN X- COS X, WHERE X LIES BETWEEN 0 AND PIE IS INCREASING OR DECREASING

ALSO TELL ME THE GENERAL WAY TO APPROACH THIS QUESTION.........

v_gurucharan

r u all dumb!!!!!!!!!!!!!!!?????????

answer yaar-----------

priyesh

for q2)
f(x) = sin x - cosx
therefore f ' (x) = cosx + sinx
therefore f' (x) is 0 at x = 3pi/4
also since sinx & cos x are +ve in first quadrant therefore it's clear that f ' (x) is +ve from 0 to 3pi/4 & -ve from 3pi/4 to pi
therefore f(x) is increasing from [0,3pi/4] & decreasing from [3pi/4 to pi]

neeraj_agarwal_1990

Just take derivative...and observe the intervals where its +ve or -ve.

or put it =0 and find if the second der. is +ve or -ve

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