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JEE Main 202229 JulyEvening Shift
Exam
JEE Main
Year
2022
Date
29 July
Shift
Evening Shift
Subject
Mathematics
Chapter
Straight Lines

JEE Main 2022 · 29 July · Evening Shift · Mathematics · Straight Lines

Let A (α, - 2), B (α, 6) and C((α)/(4), - 2) be vertices of a ∆ ABC...

Let A(α,−2),B(α,6)\left(\alpha, - 2\right), B \left(\alpha, 6\right) and C(α4,−2)C\left(\dfrac{\alpha}{4}, - 2\right) be vertices of a ∆ABC∆ ABC. If \left(5, \dfrac{\alpha}{4}\right)isthecircumcentreofis the circumcentre of∆ ABC,thenwhichofthefollowingisNOTcorrectabout, then which of the following is NOT correct about∆ ABCLet A (α, - 2), B (α, 6) and C((α)/(4), - 2) be vertices of a ∆ ABC . If (5, (α)/(4)) is the circumcentre of ∆ ABC ,

Options

  1. Aares is 2424
  2. Bperimeter is 2525
  3. Ccircumradius is 55
  4. Dinradius is 22

Correct answer

B. perimeter is 2525

Step-by-step solution

Given,

A(α,−2),B(α,6) and C(α4,−2)A\left(\alpha, - 2\right), B\left(\alpha, 6\right) \text{ and } C\left(\dfrac{\alpha}{4}, - 2\right)

Now slope of AC=0AC = 0 and slope of AB=80→∞AB = \dfrac{8}{0} \to \infty

Now we can see ACAC is perpendicular to ABAB.

So, ∆ABC∆ ABC is right angled at AA.

So, Circumcentre =mid point of BC=(5α8,2)BC = \left(\dfrac{5\alpha}{8}, 2\right)

Now given circumcentre ≡(5,α4)≡ \left(5, \dfrac{\alpha}{4}\right)

So on comparing we get,5α8=5 and α4=2\dfrac{5\alpha}{8} = 5 \text{ and } \dfrac{\alpha}{4} = 2

⇒α=8⇒ \alpha = 8

Now plotting the diagram and finding the sides with distance formula we get,

Let A (α, - 2), B (α, 6) and C((α)/(4), - 2) be vertices of a ∆ ABC . If (5, (α)/(4)) is the circumcentre of ∆ ABC ,

Area =12(6)(8)=24= \dfrac{1}{2}\left(6\right)\left(8\right) = 24

Perimeter =24= 24

Circumradius =102=5= \dfrac{10}{2} = 5

Inradius =Δs=2412=2= \dfrac{\Delta}{s} = \dfrac{24}{12} = 2

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