Decreasing functions

Asked by  | 30th Dec, 2009, 02:26: PM

Expert Answer:

df(x)/dx = 4x - (1/|x|)(x/|x|).........(since d|x|/dx = x/|x|

= 4x - x/x2 .............(Since |x||x| = x2)

= 4x - 1/x

For a decreasing function, f'(x) < 0

4x - 1/x < 0

4x2 -1 < 0

x < ±1/2

Since only in (a) this condition is met, and it's the correct answer.

Regards,

Team,

TopperLearning.

Answered by  | 31st Dec, 2009, 12:08: PM

Queries asked on Sunday & after 7pm from Monday to Saturday will be answered after 12pm the next working day.