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MHT CET · Maths · Application of Derivatives

Let \(A D\) and \(B C\) be two vertical poles at \(A\) and \(B\) respectively on a horizontal ground. If \(A D=8 \mathrm{~m}, B C=11 \mathrm{~m}\) and \(A B=10 \mathrm{~m}\), then the distance (in meters) of point \(M\) on \(A B\) from the point \(A\) such that \(M D^2+M C^2\) is minimum, is

  1. A 8
  2. B 5
  3. C 4
  4. D 7
Verified Solution

Answer & Solution

Correct Answer

(B) 5

Step-by-step Solution

Detailed explanation


\(\begin{aligned} & f(x)=M D^2+M C^2 \\ & \Rightarrow f(x)=x^2+8^2+(10-x)^2+11^2 \\ & \Rightarrow f^{\prime}(x)=2 x-2(10-x) \\ & \Rightarrow f^{\prime}(x)=4 x-20 \\ & \text { for } f(x) \text { to be minimum } x=5\end{aligned}\)