a)
{sin^2 \ 30^{\circ} + cos^2 \ 60^{\circ} - 3tg45^{\circ}=(\frac{1}{2})^2+(\frac{1}{2})^2-3\cdot 1=\frac{1}{4}+\frac{1}{4}-3=\frac{2}{4}-3=\frac{1}{2}-3=-2\frac{1}{2}=-2,5}
b)
cos69^{\circ}=sin(90^{\circ}-69^{\circ})=sin 21^{\circ}
cos73^{\circ}=sin(90^{\circ}-73^{\circ})=sin 17^{\circ}
{\frac{sin21^{\circ}}{cos69^{\circ}}+\frac{cos73^{\circ}}{sin17^{\circ}}=\frac{sin21^{\circ}}{sin21^{\circ}}+\frac{sin17^{\circ}}{sin17^{\circ}}=1+1=2}