Question

How do I work this out?

Answer 1

We can find the length of BC:

`(BC)^2+6^2=12^2\implies BC=6\sqrt3`

Then by the law of sines,

`(\sin55^\circ)/(BC)=(\sin90^\circ)/(CD)\iff CD=(6\sqrt3)/(\sin55^\circ)\approx12.7\,\mathrm{cm}`