Now, solve .

By inspection, .

Is this the only solution?

Visually, it is difficult to tell (see Fig. 1 and Fig. 2)

Fig. 1

Fig. 2

However, we can prove that is the only solution:

Fig. 3

If then from Fig. 3, we have

Area of* triangle *OAB < Area of* circular sector *OAB.

That is,

.

Hence,

If then

Put (1) and (2) together, we have

If then

i.e.,

Therefore by (3) and (4), we conclude that

only when .