Mathematics

In the diagram above, PQT is an isosceles triangle.|PQ| = |QT|, ∠SRQ = 75°, ∠QPT…

In the diagram above, PQT is an isosceles triangle.|PQ| = |QT|, ∠SRQ = 75°, ∠QPT = 25° and PQR is straight line. Find ∠RST

  • A.
    20o
  • B.
    50o
  • C.
    55o
  • D.
    70o
  • E.
    75o
Correct Answer: Option C
Explanation

< PTQ = 25° (base angles of an isos. triangle)

(therefore) < PQT = 180° – (25° + 25°) = 130° (sum of angles in triangle PQT)

(therefore) < RST = 130° – 75° = 55° (exterior angle = sum of 2 opp. interior angles)