Answer:
[tex] \sin(x) = \frac{a}{b} \\ \sin(90 - x) = \sin(90) \cos(x) - \cos(90) \sin(x) \\ \sin(90 - x) = \cos(x) \\ { \sin(x) }^{2} + { \cos(x) }^{2} = 1 \\ { \cos(x) }^{2} = 1 - {( \frac{a}{b})}^{2} = \frac{ {b}^{2} - {a}^{2} }{ {b}^{2} } \\ \cos(x) = \frac{ \sqrt{ {b}^{2} - {a}^{2} } }{ \sqrt{ {b}^{2} } } \\ \boxed{ \sin(90 - x) =\cos(x) = \frac{ \sqrt{ {b}^{2} - {a}^{2} } }{ b} } \\ [/tex]
