The equation is
and the interval
.
Consider
.
Differentiate
on each side with respect to
.

is differentiable on the interval
.
Substitute
in
.

Substitute
in
.

From above
and
.
The derivative of the function is an decreasing function.
\Hence the function
is an decreasing function.
Any decreasing function crosses the
axis only for one value of
.
Therefore the function
has at most one root in
.
The equation
has at most one root in
.