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NCERT Class XI Mathematics - Straight Lines - Solutions

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Question : 57 of 74
Marks: +1, -0
What are the points on the y-axis whose distance from the line x3+y4\frac{x}{3}+\frac{y}{4} = 1 is 4 units.
Solution:  
Given line is x3+y4\frac{x}{3}+\frac{y}{4} = 1
⇒ 4x + 3y – 12 = 0 ... (i)
Let a point on y-axis be (0, k)
If its distance from line (i) is 4 units, then
4×0+3k1242+32\left|\frac{4\times0+3k-12}{\sqrt{4^{2}+3^{2}}}\right| = 4
⇒ |3k – 12| = 4 × 5 ⇒ 3k – 12 = ± 20 ⇒ 3k = 12 ± 20
⇒ 3k = 12 + 20 or, 3k = 12 – 20 ⇒ 3k = 32 or, 3k = – 8
⇒ k = 328\frac{32}{8} or 83\frac{-8}{3}
∴ Required points are (083),(0,323)\left(0-\frac{8}{3}\right),\left(0,\frac{32}{3}\right)
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