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QJEEAdv17Mac741: JEE Advanced 2017 Mathematics - Class 12 JEEAdv17Mac741 Solution: If y = y(x) satisfies the differential equation dx, x > 0 and…

If y = y(x) satisfies the differential equation

8x(9+x)dy=(4+9+x)−1{8\sqrt x \left( {\sqrt {9 + \sqrt x } } \right)dy = {{\left( {\sqrt {4 + \sqrt {9 + \sqrt x } } } \right)}^{ - 1}}}

dx, x > 0 and y(0) = 7\sqrt 7 , then y(256) =

Multiple Choice Options

  • A 16
  • B 3
  • C 9
  • D 80

Step-by-Step Verified Solution

dydx=18x+9+x4+9+x{{dy} \over {dx}} = {1 \over {8\sqrt x + \sqrt {9 + \sqrt x } \sqrt {4 + \sqrt {9 + \sqrt x } } }}

⇒y=4++x+c\Rightarrow y = \sqrt {4 + \sqrt { + \sqrt x } } + c

Now, y(0)=7+cy(0) = \sqrt 7 + c

⇒c=0\Rightarrow c = 0

y(256)=4+9+16=4+5=3y(256) = \sqrt {4 + \sqrt {9 + \sqrt {16} } } = \sqrt {4 + 5} = 3

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