Find all real numbers
such that the equation
has no solution,
has exactly one solution,
has exactly two solutions,
has more than two solutions (in the interval
%V0
$(GDR 1)$ Find all real numbers $\lambda$ such that the equation $\sin^4 x - \cos^4 x = \lambda(\tan^4 x - \cot^4 x)$
$(a)$ has no solution,
$(b)$ has exactly one solution,
$(c)$ has exactly two solutions,
$(d)$ has more than two solutions (in the interval $(0, \frac{\pi}{4}).$
Školjka