Let a =, b = . It means that sin(a) = ; cos(b) = and "a" and "b" are the angles in QI (acute angles). Since sin(a) = cos(b), it means that a + b = . In other words, the numerator in our fraction, which is + , is equal to . Thus our original equation is = . It implies arctan(x) = = . Since arctan(x) = , it implies x = = . ANSWER. x = .