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
.