Question

In ΔABC, if m ∠A = m∠C, m∠B = ß (where ß is an acute angle), and BC = x, which expression gives the length of b, the side opposite ∠B ?
1)x2−2x2cosβ−−−−−−−−−−−√

2)x2−(1−cosβ)−−−−−−−−−−−−−√

3)2x2−(1−cosβ)2−−−−−−−−−−−−−−√

4)2x2−(1−cosβ)−−−−−−−−−−−−−−√