SI. 1 If $x^{2}-8 x+26 \equiv(x+k)^{2}+a$, find $a$.
SI. 2 If $\sin a^{\circ}=\cos b^{\circ}$, where $270<b<360$, find $b$.
SI. $3 X$ sold an article to $Y$ for $\$ b$ at a loss of $30 \%$. If the cost price of the article for $X$ is $\$ c$, find $c$.
SI. 4 In the figure, $O$ is the centre of the circle. If $\angle A C B=\frac{3 c^{\circ}}{10}$ and $\angle A O B=d^{\circ}$, find $d$.
$\begin{array}{l}x^{2}-8 x+26 \equiv(x-4)^{2}+26-16 \\ a=10 \\ \sin 10^{\circ}=\cos b^{\circ} \\ \cos b^{\circ}=\cos 80^{\circ} \\ b=360-80=280 \\ c \cdot(1-30 \%)=280 \\ c=400 \\ \angle A C B=120^{\circ} \\ \text { reflex } \angle A O B=240^{\circ}\left(\angle \text { at centre twice } \angle \text { at } \odot^{\text {ce }}\right) \\ \angle A O B=120^{\circ}(\angle \mathrm{s} \text { at a point }) \\ d=120\end{array}$