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Without using the derivative, show that the function f(x) = | x | is
A. strictly increasing in (0, ∞)
B. strictly decreasing in (-∞, 0).
We have,
f(x) = |x| =
(a)Let ,
(0,
) and
⇒
So, f(x) is increasing in (0,)
(b) Let ,
(-∞, 0)and
⇒
⇒
f(x) is strictly decreasing on(-∞, 0).