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Please solve RD Sharma class 12 Chapter maxima and minima exercise 17.5 question 1 maths textbook solution.

Answers (1)

x= \frac{15}{2}, y =\frac{15}{2}

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

Given: x+y =15

Solution: x+y =15               ..........(1)

Now,

z= x^2+y^2

z= x^2+(15-x)^2                                      (from equation 1)

z= x^2+x^2+225 -30x                          [(a-b)^2=a^2+b^2-2ab]

\frac{dz}{dx}=4x-30

For maximum or minimum value of z

\frac{dz}{dx}=0

4x-30=0

x=\frac{15}{2}

\frac{d^2z}{dx^2}=4>0

Substituting x= \frac{15}{2} in (1)

y= \frac{15}{2}

\therefore  z is minimum when x = y = \frac{15}{2}

 

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