NCERT Solution Class X Mathematics Triangles Question 1 (Ex 6.6)

Question 1:

In the given figure, PS is the bisector of ∠QPR of ΔPQR. Prove that QS/SR = PQ/PR.

Answer:

Let us draw a line segment RT parallel to SP which intersects extended line segment QP at point T.

Given that, PS is the angle bisector of ∠QPR.

∠QPS = ∠SPR … (1)

By construction,

∠SPR = ∠PRT (As PS || TR) … (2)

∠QPS = ∠QTR (As PS || TR) … (3)

Using these equations, we obtain

∠PRT = ∠QTR

∴ PT = PR

By construction,

PS || TR

By using basic proportionality theorem for ΔQTR,

QS/SR = QP/PT

⇒ QS/SR = PQ/PR  (PT = TR)

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