Question:

Let \(\mathrm{P}\) be a point in the first quadrant lying on the ellipse \(9x^{2}+16y^{2}=144\), such that the tangent at \(\mathrm{P}\) to the ellipse is inclined at an angle \(135^{\circ}\) to the positive direction of \(x\)-axis. Then the coordinates of \(\mathrm{P}\) are :

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Differentiate the ellipse equation to get the tangent slope, set it equal to \(\tan 135^{\circ}=-1\), and combine with the ellipse equation.
Updated On: Nov 12, 2026
  • \(\left(\frac{\sqrt{143}}{3},\frac{1}{4}\right)\)
  • \(\left(\frac{8}{9},\frac{\sqrt{77}}{3}\right)\)
  • \(\left(\frac{4}{\sqrt{2}},\frac{3}{\sqrt{2}}\right)\)
  • \(\left(\frac{16}{5},\frac{9}{5}\right)\)
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The Correct Option is D

Solution and Explanation

Differentiating \(9x^{2}+16y^{2}=144\): \(18x+32y\,\frac{dy}{dx}=0\Rightarrow \frac{dy}{dx}=-\frac{9x}{16y}\).
Tangent slope \(=\tan135^{\circ}=-1\Rightarrow 9x=16y\Rightarrow x=\frac{16y}{9}\).
Substituting: \(9\cdot\frac{256y^{2}}{81}+16y^{2}=144\Rightarrow \frac{256y^{2}}{9}+\frac{144y^{2}}{9}=144\Rightarrow y^{2}=\frac{81}{25}\).
First quadrant: \(y=\frac{9}{5}\), \(x=\frac{16}{5}\).
Answer: (4) \(\left(\frac{16}{5},\frac{9}{5}\right)\)
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