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JEE Main 201910 JanuaryMorning Shift
Exam
JEE Main
Year
2019
Date
10 January
Shift
Morning Shift
Subject
Mathematics
Chapter
Straight Lines

JEE Main 2019 · 10 January · Morning Shift · Mathematics · Straight Lines

If the line 3x + 4y - 24 = 0 intersects the x -axis is at the point...

If the line 3x+4y−24=03x + 4y - 24 = 0 intersects the xx-axis is at the point AA and the yy-axis at the point B,B, then the incentre of the triangle OAB,OAB, where OOis the origin, is:If the line 3x + 4y - 24 = 0 intersects the x -axis is at the point A and the y -axis at the point B, then the incentre

Options

  1. A(4,4)\left(4, 4\right)
  2. B(3,4)\left(3, 4\right)
  3. C(4,3)\left(4, 3\right)
  4. D(2,2)\left(2, 2\right)

Correct answer

D. (2,2)\left(2, 2\right)

Step-by-step solution

The xx intercept of the line 3x+4y−24=03x + 4y - 24 = 0 can be obtained by putting y=0y = 0 i.e. 3x−24=03x - 24 = 0

⇒x=8⇒ x = 8

Hence, the point AA is \left(8, 0\right) .</p><p>Now,the</p><p>Now, theyinterceptofthelineintercept of the line3x + 4y - 24 = 0canbeobtainedbyputtingcan be obtained by puttingx = 0i.e.i.e.4y - 24 = 0</p><p></p><p>⇒ y = 6</p><p>Hence,thepoint</p><p>Hence, the pointBis(0,6).is \left(0, 6\right) .

If the line 3x + 4y - 24 = 0 intersects the x -axis is at the point A and the y -axis at the point B, then the incentre

In ∆OAB,∆ OAB, we have OA=b=8,OB=a=6OA = b = 8, OB = a = 6 and AB=c=(8−0)2+(0−6)2=64+36=10AB = c = \sqrt{{\left(8 - 0\right)}^{2} + {\left(0 - 6\right)}^{2}} = \sqrt{64 + 36} = 10 units.

And, we know that the co-ordinates of incentre II of a triangle with vertices \left({x}_{1}, {y}_{1}\right), \left({x}_{2}, {y}_{2}\right)and(x3,y3)and \left({x}_{3}, {y}_{3}\right) and having length of the sides opposite to these vertices as a,ba, b and c,c, respectively, is

I≡(ax1+bx2+cx3a+b+c,ay1+by2+cy3a+b+c)I ≡ \left(\dfrac{a{x}_{1} + b{x}_{2} + c{x}_{3}}{a + b + c}, \dfrac{a{y}_{1} + b{y}_{2} + c{y}_{3}}{a + b + c}\right)

⇒I≡(6(8)+8(0)+10(0)24,6(0)+8(6)+10(0)24)⇒ I ≡ \left(\dfrac{6\left(8\right) + 8\left(0\right) + 10\left(0\right)}{24}, \dfrac{6\left(0\right) + 8\left(6\right) + 10\left(0\right)}{24}\right)

⇒I=(2,2).⇒ I = \left(2, 2\right) .

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