2. In the diagram below, angle AOB = 66°
Find angle OAB, giving reasons for your answer.

57°

Step-by-step explanation:

Δ AOB has 2 equal sides as radius of the circle, this is isosceles triangle

So the angles ∠OAB= ∠OBA

∠AOB= 66° and sum of 3 angles = 180°

So  ∠OAB= (180° - 66°)/2= 57°

we have three similar triangles, because each has a right angle and shares an angle.   let's write the angles in order: opposite to short leg, long leg, hypotenuse.

cab similar to bad similar to cbd

or as ratios,

ca: ab: cb = ba: ad: bd = cb: bd: cd

we also know

ac = ad + cd

(ad+cd): ab: cb = ba: ad: bd = cb: bd: cd

(ad+cd)/cb=cb/cd

we have cb=6, ad=5 and seek x=cd.

we reject the negative root and conclude x=4

answer: 4