Construct ΔPQR if PQ = 5 cm, m∠PQR = 105° and m∠QRP = 40°.

(Hint: Recall angle sum property of a triangle).

A rough sketch of the required ΔPQR is as follows.

In order to construct ΔPQR, the measure of ∠RPQ has to be calculated.

According to the angle sum property of triangles,

∠PQR + ∠PRQ + ∠RPQ = 180º

105º + 40º + ∠RPQ = 180º

145º + ∠RPQ = 180º

∠RPQ = 180° − 145° = 35°

The steps of construction are as follows.

(i) Draw a line segment PQ of length 5 cm.

(ii) At P, draw a ray PX making an angle of 35º with PQ.

(iii) At point Q, draw a ray QY making an angle of 105º with PQ.

(iv)Point R has to lie on both the rays, PX and QY. Therefore, R is the point of intersection of these two rays.

This is the required triangle PQR.

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