How do you find the domain and range of h(x) = log_3[x/(x - 1)]?

1 Answer
Jul 25, 2018

The domain is x in (-oo,0) uu(1,+oo). The range is y in (-oo,0)uu(0,+oo)

Explanation:

What's under the log must be >0

Therefore,

x/(x-1)>0

Let g(x)=x/(x-1)

Make a sign chart to solve this inequality

color(white)(aaaa)xcolor(white)(aaaa)-oocolor(white)(aaaaa)0color(white)(aaaaaaaa)1color(white)(aaaaaaaa)+oo

color(white)(aaaa)xcolor(white)(aaaaaaaa)-color(white)(aaaaa)+color(white)(aaaaaaaa)+

color(white)(aaaa)x-1color(white)(aaaaa)-color(white)(aaaa)-color(white)(aaaa)||color(white)(aaaa)+

color(white)(aaaa)g(x)color(white)(aaaaaa)+color(white)(aaaa)-color(white)(aaaa)||color(white)(aaaa)+

Therefore,

g(x)>0 when x in (-oo,0) uu(1,+oo)

The domain is x in (-oo,0) uu(1,+oo)

To find the range, let

y=log_3(x/(x-1))

So,

By the definition of the logarithm

x/(x-1)=3^y

x=3^y(x-1)

x3^y-x=3^(y)

x(3^y-1)=3^y

x=3^y/(3^y-1)

The denominator must be !=0

3^y-1!=0

=>, y!=0

The range is y in (-oo,0)uu(0,+oo)

graph{log(x/(x-1)) [-8.89, 8.886, -4.45, 4.44]}