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Please solve RD Sharma class 12 Chapter maxima and minima exercise 17.5 question 29 maths textbook solution.

Answers (1)

(\pm 2\sqrt{3},3)

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=4y  nearest to (0,5)

x^2=4y

y=\frac{x^2}{4}                          .........(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}{4} -5\right )^2                     ....... from (1)

\begin{aligned} &=x^{2}+\frac{x^{4}}{16}+25-\frac{5 x^{2}}{2} \\ &\frac{d z}{d y}=2 x+\frac{4 x^{3}}{16}-5 x \\ &\frac{d z}{d y}=0 \\ &2 x+\frac{4 x^{3}}{16}-5 x=0 \end{aligned}

\frac{4x^3}{16}=3x

x^3=12x

x^2=12

x=\pm 2\sqrt{3}

Substituting the value of x is equal (1)

y =3

\frac{d^{2} z}{d y^{2}}=2+\frac{12 x^{2}}{16}-5=9-3=6>0

The required nearest point is (\pm 2\sqrt{3},3)

 

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infoexpert24

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