Add fractions (remember commom denominator ):Originally Posted byling_c_0202

But the numerator is expansion of

Thus, you have,

Multiply both sides by a half to get,

But, and (double angles),

Notice the kills the other thus,

Thus,

Thus, all the solutions take the form,

Thus,

You need them to be such as,

For the example the top solution is true only for otherwise it gets too big or too small. Substituting for the top solution we get,

The bottom solution is true only for otherwise it gets too big or too small. Substituting for the bottom solution we get,

Thus,