Question 35
In the unit circle shown in the figure, chords $PQ$ and $MN$ are parallel to the unit radius $OR$ of the circle with center at $O.$ Chords $MP,$ $PQ,$ and $NR$ are each $s$ units long and chord $MN$ is $d$ units long.
Of the three equations $$
\begin{array}{rl} \mathrm{I}.&d-s=1,\\ \mathrm{II}.&ds=1,\\ \mathrm{III}.&d^2-s^2=\sqrt5 \end{array}
$$ those which are necessarily true are
Of the three equations $$
\begin{array}{rl} \mathrm{I}.&d-s=1,\\ \mathrm{II}.&ds=1,\\ \mathrm{III}.&d^2-s^2=\sqrt5 \end{array}
$$ those which are necessarily true are