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Find the point on the curve x2 + y2 = 13, the tangent at each one of which is parallel to the line 2x + 3y = 7. |
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Answer» Given: The curve x2 + y2 = 13 and the line 2x + 3y = 7 x2 + y2 = 13 Differentiating the above w.r.t x ⇒ 2x2 – 1 + 2y2 – 1 \(\frac{dy}{dx}\)= 0 ⇒ 2x + 2y\(\frac{dy}{dx}\) = 0 ⇒ 2(x + y\(\frac{dy}{dx}\) ) = 0 ⇒ (x + y\(\frac{dy}{dx}\) ) = 0 ⇒ y\(\frac{dy}{dx}\)= – x ⇒ \(\frac{dy}{dx}\) = \(\frac{-x}{y}\)...(1) Since, line is 2x + 3y = 7 ⇒ 3y = – 2x + 7 ⇒ y = \(\frac{-2x+7}{3}\) ⇒ y = \(\frac{-2x}{3}+\frac{7}{3}\) \(\therefore\) The equation of a straight line is y = mx + c, where m is the The Slope of the line. Thus, the The Slope of the line is \(\frac{-2}{3}\)...(2) Since, tangent is parallel to the line, \(\therefore\) the The Slope of the tangent = The Slope of the normal \(\frac{-x}{y}\) = \(\frac{-2}{3}\) ⇒ – x = \(\frac{-2y}{3}\) ⇒ x = \(\frac{2y}{3}\) Substituting x = \(\frac{2y}{3}\) in x2 + y2 = 13, ⇒ ( \(\frac{2y}{3}\) )2 + y2 = 13 ⇒ ( \(\frac{4y^2}{3}\) ) + y2 = 13 ⇒ y2( \(\frac{4}{9}+1\) ) = 13 ⇒ y2( \(\frac{13}{9}\) ) = 13 ⇒ y2( \(\frac{1}{9}\) ) = 1 ⇒ y2 = 9 ⇒ y = \(\pm\)3 Substituting y = \(\pm\)3 in x = \(\frac{2y}{3}\),we get, x = \(\frac{2x(\pm3)}{3}\) x = \(\pm\)2 Thus, the required point is (2, 3) & ( – 2, – 3) |
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