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Please solve RD Sharma class 12 Chapter maxima and minima exercise 17.5 question 30 maths textbook solution.

Answers (1)

(4,-4)

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

Given: y^2=4x

x=\frac{y^2}{4}               ........(1)

Also,

d^2=(x-2)^2+(y+8)^2 using distance formula

Solution:

Now,

z=d^2=(x-2)^2+(y+8)^2

z=\left ( \frac{y^2}{4}-2 \right )^2+(y+8)^2             ...... from (1)

\begin{aligned} &=\frac{y^{4}}{16}+4-y^{2}+y^{2}+54+16 y \\ &\frac{d z}{d y}=\frac{4 y^{3}}{16}+16 \\ &\frac{d z}{d y}=0 \\ &\frac{4 y^{3}}{16}+16=0 \end{aligned}

4y^3=-64, y=-4

Substituting the value of y in equation (1)

x =4

\frac{d^{2} z}{d y^{2}}=\frac{12 y^{2}}{16}=12>0

The required nearest point is (4,-4)

 

 

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infoexpert24

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