Examine that sin | x| is a continuous function.
It is given that f(x) = sin|x|
The given function f is defined for real number and f can be written as the composition of two functions, as
f = goh, where g(x) = |x| and h(x) = sinx
First we have to prove that g(x) = |x| and h(x) = sinx are continuous functions.
g(x) = |x| can be written as
Now, g is defined for all real number.
Let k be a real number.
Case I: If k < 0,
Then g(k) = -k
And
Thus,
Therefore, g is continuous at all points x, i.e., x > 0
Case II: If k > 0,
Then g(k) = k and
Thus,
Therefore, g is continuous at all points x, i.e., x < 0.
Case III: If k = 0,
Then, g(k) = g(0) = 0
Therefore, g is continuous at x = 0
From the above 3 cases, we get that g is continuous at all points.
h(x) = sinx
We know that h is defined for every real number.
Let k be a real number.
Now, put x = k + h
If
= sinkcos0 + cosksin0
= sink
Thus, h(x) = cosx is continuous function.
We know that for real valued functions g and h, such that (goh) is defined at k, if g is continuous at k and if f is continuous at g(k),
Then (fog) is continuous at k.
Therefore, f(x) = (gof)(x) = g(h(x)) = g(sinx) = |sinx| is a continuous function.