First subtract 2 revolutions from the - 840 :- (- (840-720) = -120
This gives sin -120 which is in the 3rd quadrant of the unit circle
sin -120 = - sin 60 = - sqrt3/2
Answer:
the correct answer is (b).........
the triangle could only be proven isosceles if it was proven or given that SP = SR or thatangles PQS = RQS otherwise the reasoning is incomplete