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ΔPQR is an isosceles triangle such that PQ = QR. If S is a point on QR produced such that PR = RS and ∠QPS = 63°, find ∠PSQ.

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Answer

ΔPQR is an isosceles triangle such that PQ = QR.

S is a point on QR produced such that PR = RS.

ΔPQR is an isosceles triangle such that PQ = QR. If S is a point on QR produced such that PR = RS and ∠QPS = 63°, find ∠PSQ. Triangles, ML Aggarwal Understanding Mathematics Solutions ICSE Class 9.

As we know that in an isosceles triangle, angles opposite to equal sides are equal.

In ΔPQR,

⇒ ∠QPR = ∠QRP = x° (let)………………..(1)

In ΔPRS,

⇒ ∠PSR = ∠SPR = y° (let)………………..(2)

Given,

⇒ ∠QPS = 63°

From figure,

⇒ ∠QPR + ∠SPR = 63°

⇒ x° + y° = 63° ………………(3)

We know that,

The exterior angle of a triangle is equal to the sum of the two opposite interior angles.

The angle ∠PRQ (which is x) is an exterior angle to △PRS at vertex R.

⇒ ∠PRQ = ∠SPR + ∠PSR.

⇒ x° = y° + y°

⇒ x° = 2y°

Substituting the above value of x in equation (1), we get :

⇒ 2y° + y° = 63°

⇒ 3y° = 63°

⇒ y° = 63°3\dfrac{63°}{3}

⇒ y° = 21°

⇒ ∠PSR = ∠SPR = 21°.

From figure,

⇒ ∠PSQ = ∠PSR = 21°

Hence, ∠PSQ = 21°.

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