<s>[INST] Length of chord in circle 

*In Figure 3, arc CD is a semicircle. AB is perpendicular to CD, BC = 3, BD = 4. Then the length of AB =


a) 3.25   b) 4.56   c) 3.46  d) 7.00

 [/INST] HINT : 
Note that $\angle CAD=90^\circ$, and so $AC^2+AD^2=CD^2$.
Letting $AB=x$, since
$$AC^2=x^2+3^2, AD^2=x^2+4^2, CD^2=7^2$$
you'll get an equation of $x$ as
$$7^2=9+x^2+x^2+16\iff x^2=12.$$
</s>