The following questions have three statements. Study the question and the statements and decide which of the statement(s) is/are necessary to answer the question. Find the area of the isosceles triangle. I: The length of median to the side opposite to the single largest angle in the triangle is 3√5 cm. II: The length of the side opposite to the single largest angle in the triangle is 12 cm. III: The perimeter of the triangle is 30 cm.
The following questions have three statements. Study the question and the statements and decide which of the statement(s) is/are necessary to answer the question. Find the area of the isosceles triangle. I: The length of median to the side opposite to the single largest angle in the triangle is 3√5 cm. II: The length of the side opposite to the single largest angle in the triangle is 12 cm. III: The perimeter of the triangle is 30 cm. Correct Answer Any two statements are sufficient to answer the question.
Statement I and II:
The length of median to the side opposite to the single largest angle in the triangle is 3√5 cm and the length of the side opposite to the single largest angle in the triangle is 12 cm;
Side opposite to the single largest angle will be longest.
[ alt="22.10.2018.0076" src="//storage.googleapis.com/tb-img/production/18/10/22.10.2018.0076.PNG" style="height:155px; width:249px">
From the figure:
We can find the value of AB and AC using Pythagoras theorem.
∴The area of the triangle can be find out with help of lengths of all three sides.
Statement II and III:
The length of the side opposite to the single largest angle in the triangle is 12 cm and perimeter of the triangle is 30 cm;
∴ The equal sides of the triangle = (30 – 12)/2 = 9 cm
∴ The area of the triangle can be find out with help of lengths of all three sides.
Statement I and III:
AB + BC + AC = 30
⇒ 2AB + BC = 30
⇒ AB = (30 – BC)/2 ----(1)
Using Apollonius’ theorem
AB2 + AC2 = 2CD2 + 2AD2
⇒ 2AB2 = 2CD2 + 2AD2 (∵ ΔABC is isosceles triangle)
⇒ AB2 – (BC/2)2 = AD2 (∵ 2CD = BC)
⇒ (30 – BC)2 – BC2 = 4(3√5)2 {from eq. (1)}
⇒ 900 + BC2 – 60BC – BC2 = 180
⇒ BC = 12 cm
Area of triangle = 1/2 × BC × AD = 1/2 × 12 × 3√5
∴ Any two of the statements are sufficient to answer the question