(a(i))[1]
State the mathematical name of line $OB$.
(a(ii))[1]
State the reason why angle $ABO$ is $90^\circ$.
(a(iii))[1]
Find angle $AOB$.
(a(iv))[1]
State the reason why angle $ADC$ = angle $AOB$.
(a(v))[1]
Complete the statement by inserting a mathematical word. Triangle $AOB$ is [BLANK] to triangle $ADC$.
(a(vi))[6]
Calculate the values of $OB$, $OA$ and the area of triangle $AOB$.
(b)[1]
Show that the interior-angle sum of this polygon equals $900^\circ$.