Question : ABC is an isosceles triangle inscribed in a circle. If AB = AC = $12\sqrt{5}$ cm and BC = 24 cm, then the radius of circle is:
Option 1: 10 cm
Option 2: 15 cm
Option 3: 12 cm
Option 4: 14 cm
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Correct Answer: 15 cm
Solution : Given, AB = AC = 1$2\sqrt{5}$cm and BC = 24 cm Join OB, OC, and OA. Draw AD$\perp$ BC which will pass through centre O OD bisects BC in D as perpendicular from the centre to a chord bisects the chord. So, BD = CD = 12 cm Using Pythagoras theorem in $\triangle$ ABD, AB2 = AD2 + BD2 Or, $(12\sqrt{5})^{2}$ = AD2 + 122 Or, AD2 = 576 Or, AD = 24 cm Let the radius of the circle be OA = OB = OC = r So, OD = AD – AO = 24 – r Using Pythagoras theorem in $\triangle$ OBD, r2 =122 + (24 – r)2 Or, r2 = 144 + 576 + r2 – 48r Or, r = 15 cm Hence, the correct answer is 15 cm.
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Question : $\triangle ABC$ is an isosceles triangle with AB = AC = 15 cm and an altitude from A to BC of 12 cm. The length of side BC is:
Option 1: 9 cm
Option 2: 12 cm
Option 3: 18 cm
Option 4: 20 cm
Question : ABC is an isosceles right-angle triangle. $\angle ABC = 90 ^{\circ}$ and AB = 12 cm. What is the ratio of the radius of the circle inscribed in it to the radius of the circle circumscribing $\triangle ABC$?
Option 1: $6–\sqrt{2}: 3 \sqrt{2}$
Option 2: $2–\sqrt{2}: \sqrt{2}$
Option 3: $6–3 \sqrt{2}: 1 \sqrt{2}$
Option 4: $6–3 \sqrt{2}: 6 \sqrt{2}$
Question : $O$ is the circumcentre of the isosceles $\triangle ABC$. Given that $AB = AC = 5$ cm and $BC = 6$ cm. The radius of the circle is:
Option 1: 3.015 cm
Option 2: 3.205 cm
Option 3: 3.025 cm
Option 4: 3.125 cm
Question : A circle is inscribed in a ΔABC having sides AB = 16 cm, BC = 20 cm, and AC = 24 cm, and sides AB, BC, and AC touch circle at D, E, and F, respectively. The measure of AD is:
Option 2: 20 cm
Option 3: 6 cm
Question : In a triangle ${ABC}, {AB}={AC}$ and the perimeter of $\triangle {ABC}$ is $8(2+\sqrt{2}) $ cm. If the length of ${BC}$ is $\sqrt{2}$ times the length of ${AB}$, then find the area of $\triangle {ABC}$.
Option 1: $32 \ cm^2$
Option 2: $28 \ cm^2$
Option 3: $16 \ cm^2$
Option 4: $36 \ cm^2$
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