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Please solve RD Sharma class 12 Chapter maxima and minima exercise 17.5 question 32 maths textbook solution.

Answers (1)

(\pm 2\sqrt{2},4)

Hint: For maximum or minimum value of z must have \frac{dz}{dy}=0

Given: Let the point (x,y) on the curve x^2=2y nearest (0,5)

x^2=2y

y=\frac{x^2}{2}                    .........(1)

Also,

d^2=(x)^2+(y-5)^2  using the distance formula

 

Solution: 

Now,

z=d^2=(x)^2+(y-5)^2

z=(x)^2+\left ( \frac{x^2}{2}-5 \right )^2                 ....... from (1)

\begin{aligned} &=x^{2}+\frac{x^{4}}{4}+25-5 x^{2} \\ &\frac{d z}{d y}=2 x+x^{3}-10 x \\ &\frac{d z}{d y}=0 \\ &x^{3}-8 x=0 \\ &x^{2}=8, x=\pm 2 \sqrt{2} \end{aligned}

Substituting the value of x in eqn (1)

y =4

\frac{d^2z}{dy^2}=3x^2-8

=24-8=16>0

The required nearest point (\pm 2\sqrt{2},4)

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infoexpert24

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