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If a curve passes through the origin and the slope of the tangent to it at any point (x, y) is $${{{x^2} - 4x + y + 8} \over {x - 2}}$$, then this curve also passes through the point :

JEE · Math · previous-year question

  1. A.(4, 4)
  2. B.(5, 5)correct
  3. C.(5, 4)
  4. D.(4, 5)

Answer

B. (5, 5)

Explanation

Given y (0) = 0 & $${{dy} \over {dx}} = {{{{(x - 2)}^2} + y + 4} \over {x - 2}}$$ $$ \Rightarrow {{dy} \over {dx}} - {y \over {x - 2}} = (x - 2) + {4 \over {x - 2}}$$ $$ \Rightarrow I.F. = {e^{ - \int {{1 \over {x - 2}}dx} }} = {1 \over {x - 2}}$$ Solution of D.E. $$ \Rightarrow y.{1 \over {x - 2}} = \int {{1 \over {x - 2}}\left( {(x - 2) + {4 \over {x - 2}}} \right)} \,.\,dx$$ $$ \Rightarrow {y \over {x - 2}} = x - {4 \over {x - 2}} + C$$ Now, at x = 0, y = 0 $$ \Rightarrow $$ C = $$-$$2 $$ \therefore $$ y = x (x $$-$$ 2) $$-$$ 4 $$-$$ 2 (x $$-$$ 2) $$ \Rightarrow $$ y = x2 $$-$$ 4x This curve passes through (5, 5)

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