Question

Which do the following options represent the measure of arc RA

A.38.6
B.65.6
C.71.4
D.77.2

Answer 1

77.2°

Explanation:

Consider the triangle JKR.

∠KJR=108.6 (lies on the same line as ∠RJA, angles on a straight line add up to 180)

All the angles in a triangle add up to 180, so:

∠JKR+∠KJR+∠JRK=180

∠JKR+108.6+32.8=180

∠JKR=38.6=∠RKA

Consider ∠RKA. This angle stands on the same arc as ∠RCA.

Since the angle at centre is twice the angle at circumference, 2(∠RKA) = ∠RCA.

2(∠RKA) = ∠RCA

2(38.6)=∠RCA

∠RCA=77.2°