1.

Show that line x – 3y – 4 = 0 touches ellipse 3x2 + 4y2 = 20.

Answer»

Equation of line, x – 3y – 4 =0

⇒ x = 3y + 4

Equation of ellipse,

3x2 + 4y2 = 20

Putting value of x from (i) in eqn. (ii),

3(3y + 4)2 + 4y2 = 20

⇒ 3(9y2 + 24y + 16) + 4y2 – 20 = 0

⇒ 27y2 + 72y + 48 + 4y2 – 20 = 0

⇒ 31y2 + 72y + 28 = 0

Line will touch eqn. (ii) if

(72)2 – 4(31 )(28) = 0

∴ (72)2 – 4 × 31 × 28 = 5184 – 3472

= 1712 ≠ 0

Thus, given line will not be touch given ellipse.

∴ Given equation is wrong.



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