Question : $\triangle$ PQR circumscribes a circle with centre O and radius r cm such that $\angle$ PQR = $90^{\circ}$. If PQ = 3 cm, QR = 4 cm, then the value of r is:
Option 1: 2
Option 2: 1.5
Option 3: 2.5
Option 4: 1
Correct Answer: 1
Solution : PQ = 3 cm, QR = 4 cm OB = OA = OC = r Since tangents drawn from a point to the circle are equal, AQ = QB = $r$ ⇒ PA = PC = $3-r$ ⇒ RC = RB = $4-r$ By Pythagoras theorem, PR2 = QR2 + PQ2 ⇒ PR = $\sqrt{9+16}$ = 5 cm ⇒ PR = PC + CR ⇒ 5 = $3-r$ + $4-r$ ⇒ $2r$ = 7–5 = 2 ⇒ $r$ = 1 cm Hence, the correct answer is 1.
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Question : In $\triangle$PQR, $\angle$ PQR = $90^{\circ}$, PQ = 5 cm and QR = 12 cm. What is the radius (in cm) of the circumcircle of $\triangle$PQR?
Option 1: 6.5
Option 2: 7.5
Option 3: 13
Option 4: 15
Question : In a $\triangle P Q R, \angle P: \angle Q: \angle R=3: 4: 8$. The shortest side and the longest side of the triangle, respectively, are:
Option 1: PQ and PR
Option 2: QR and PR
Option 3: PQ and QR
Option 4: QR and PQ
Question : In $\Delta PQR,$ $\angle P : \angle Q : \angle R = 1: 3 : 5$, what is the value of $\angle R - \angle P$?
Option 1: $30^\circ$
Option 2: $80^\circ$
Option 3: $45^\circ$
Option 4: $60^\circ$
Question : ABC is a right-angled triangle with AB = 6 cm and BC = 8 cm. A circle with centre O has been inscribed inside $\triangle ABC$. The radius of the circle is:
Option 1: 1 cm
Option 2: 2 cm
Option 3: 3 cm
Option 4: 4 cm
Question : In a triangle ABC, if $\angle B=90^{\circ}, \angle C=45^{\circ}$ and AC = 4 cm, then the value of BC is:
Option 1: $\sqrt{2} \mathrm{~cm}$
Option 2: $4 \mathrm{~cm}$
Option 3: $2 \sqrt{2} \mathrm{~cm}$
Option 4: $4 \sqrt{2} \mathrm{~cm}$
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