The expression is .

(a)

Intermediate value theorem :

The function is continuous on the closed interval , let be the number between  and , where then exist a number in such that .

Consider the function is .

Consider the function to be continuous over the interval .

Prove that the number exists between  and .

.

Substitute in the function.

.

.

Substitute in the function.

.

Thus, .

Then according to intermediate value theorem, there exist at least one root between and such that .

(b)

Graph :

Graph the function :

Observe the graph.

.

Therefore the root of the function is .

The root of the function is .