In the diagram above, PQT is an isosceles triangle.|PQ| = |QT|, ∠SRQ = 75^\circ, ∠QPT = 25^\circ and PQR is straight line. Find ∠RST
Attached Figure / Diagram
A
20o
B
50o
C
55o
D
70o
E
75o
Verified Correct Answer: C.
Step-by-Step Mathematical Solution
< PTQ = 25^\circ (base angles of an isos. triangle)
\(\therefore\) < PQT = 180^\circ - (25^\circ + 25^\circ) = 130^\circ (sum of angles in triangle PQT)
\(\therefore\) < RST = 130^\circ - 75^\circ = 55^\circ (exterior angle = sum of 2 opp. interior angles)
Source: Myschool Past Questions Archive (Record #23166)