Q31 / 51 · JEE Advanced 2023 (Paper 2) · Mathematics

Consider an obtuse angled triangle ABC in which the difference between the largest and the smallest angle is π2 and whose sides are in arithmetic progression. Suppose that the vertices of this triangle lie on a circle of radius 1.
(There are two questions based on PARAGRAPH " 1 ", the question given below is one of them)
Let α be the area of the triangle ABC. Then the value of (64α)2 is

Correct answer: 1008

Solution

Let angle A be obtuse angle and let sides be a-d, a, a+d

So, plotting the diagram we get,

Figure

Now let sides be, a−d,a,a+d

Also given angle A−C=π2

And circum radius R=1

Now by sine rule we get,

a+dsin⁡A=asin⁡B=a−dsin⁡C=2

∵A=π2+C

⇒sin⁡A=sin⁡π2+C

⇒sin⁡A=cos⁡C

⇒a+d2=1−sin2⁡C

⇒a+d22=1-a-d22

⇒2a2+d24=1

⇒a2+d2=2    ...(1)

Now using cosine rule we get,

cos⁡B=(a−d)2+(a+d)2−a22a2−d2

⇒1-sin2B=2a2+d2-a22a2-d2

⇒1-a24=4-a22a2-d2  ∵a2+d2=2

⇒a2-d22=4-a2    ...(2)

From (1) & (2)
a2=74,d2=14
Area of triangle
Δ=aa2-d24

α=72×64×4

Now 64α2=64×64×74×3616×16=4×252=1008

Hence, the correct answer is 1008.

More Properties of Triangles Questions