JEE MAIN - Mathematics (2022 - 30th June Morning Shift - No. 9)

Let $$\alpha$$1, $$\alpha$$2 ($$\alpha$$1 < $$\alpha$$2) be the values of $$\alpha$$ fo the points ($$\alpha$$, $$-$$3), (2, 0) and (1, $$\alpha$$) to be collinear. Then the equation of the line, passing through ($$\alpha$$1, $$\alpha$$2) and making an angle of $${\pi \over 3}$$ with the positive direction of the x-axis, is :
$$x - \sqrt 3 y - 3\sqrt 3 + 1 = 0$$
$$\sqrt 3 x - y + \sqrt 3 + 3 = 0$$
$$x - \sqrt 3 y + 3\sqrt 3 + 1 = 0$$
$$\sqrt 3 x - y + \sqrt 3 - 3 = 0$$

Explanation

Points A($$\alpha$$, $$-$$3), B(2, 0) and C(1, $$\alpha$$) are collinear.

JEE Main 2022 (Online) 30th June Morning Shift Mathematics - Straight Lines and Pair of Straight Lines Question 55 English Explanation

$$\therefore$$ Slope of AB = Slope of BC

$$ \Rightarrow {{0 + 3} \over {2 - \alpha }} = {{\alpha - 0} \over {1 - 2}}$$

$$ \Rightarrow - 3 = \alpha (2 - \alpha )$$

$$ \Rightarrow - 3 = 2\alpha - {\alpha ^2}$$

$$ \Rightarrow {\alpha ^2} - 2\alpha - 3 = 0$$

$$ \Rightarrow {\alpha ^2} - 3\alpha + \alpha - 3 = 0$$

$$ \Rightarrow \alpha (\alpha - 3) + 1(\alpha - 3) = 0$$

$$ \Rightarrow (\alpha + 1)(\alpha - 3) = 0$$

$$ \Rightarrow \alpha = - 1,\,3$$

Given, $${\alpha _1} < {\alpha _2}$$

$$\therefore$$ $${\alpha _1} = -1$$ and $${\alpha _2} = 3$$

$$\therefore$$ $$\left( {{\alpha _1},\,{\alpha _2}} \right) = ( - 1,\,3)$$

Now, equation of the line passing through ($$-$$1, 3) and making angle $${\pi \over 3}$$ with positive x-axis is

$$(y - {y_1}) = m(x - {x_1})$$

$$ \Rightarrow y - 3 = \left( {\tan {\pi \over 3}} \right)(x + 1)$$

$$ \Rightarrow y - 3 = \sqrt 3 (x + 1)$$

$$ \Rightarrow \sqrt 3 x - y + \sqrt 3 + 3 = 0$$

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