If xm yn = (x + y)m + n, prove that  from Mathematics Applicat

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 Multiple Choice QuestionsShort Answer Type

411.

Show that the function f(x) = 4x3 – 18x2 + 27x – 7 is always increasing on R.

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412.

Differentiate the function (sin x)x + sin–1 √xwith respect to x.

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413.

If xm yn = (x + y)m + n, prove that fraction numerator straight d squared straight y over denominator dx squared end fraction space equals space 0


We are given,
If xm yn = (x + y)m + n

Taking log on both sides, we get
log xm yn = log(x + y)m + n
log xm + log yn = m+n log(x + y)
m logx + n logy = m+n log (x+y)

Differentiating above equation w.r.t. x, we get

 straight m over straight x space plus straight n over straight y dy over dx space equals space fraction numerator left parenthesis straight m plus straight n right parenthesis over denominator left parenthesis straight x plus straight y right parenthesis end fraction space space straight x space open parentheses 1 plus dy over dx space close parentheses
straight n over straight y dy over dx minus open parentheses fraction numerator straight m plus straight n over denominator straight x plus straight y end fraction close parentheses dy over dx space equals space open parentheses fraction numerator straight m plus straight n over denominator straight x plus straight y end fraction close parentheses minus straight m over straight x
open parentheses straight n over straight y minus fraction numerator straight m plus straight n over denominator straight x plus straight y end fraction close parentheses dy over dx space equals space fraction numerator straight x left parenthesis straight m plus straight n right parenthesis minus straight m left parenthesis straight x plus straight y right parenthesis over denominator straight x left parenthesis straight x plus straight y right parenthesis end fraction
open parentheses fraction numerator nx plus ny minus my minus ny over denominator straight y left parenthesis straight x plus straight y right parenthesis end fraction close parentheses dy over dx space equals space fraction numerator xm plus xn minus mx space minus my over denominator straight x space left parenthesis straight x plus straight y right parenthesis end fraction
dy over dx space equals space straight y over straight x space straight x fraction numerator left parenthesis xn minus my right parenthesis over denominator left parenthesis xn minus my right parenthesis end fraction
rightwards double arrow space dy over dx space equals space straight y over straight x
And fraction numerator begin display style space straight d squared straight y end style over denominator dx squared end fraction space equals space fraction numerator straight x begin display style dy over dx end style minus straight y over denominator straight x squared end fraction
space equals space fraction numerator straight x begin display style straight y over straight x end style minus straight y over denominator straight x squared end fraction
space equals space 0

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 Multiple Choice QuestionsLong Answer Type

414.

If the sum of lengths of the hypotenuse and a side of a right angled triangle is given, show that the area of the triangle is maximum, when the angle between them is π/3.

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415.

Solve the differential equation straight x dy over dx space plus straight y space equals space straight x space cos space straight x space plus space sin space straight x comma space given space that space straight y space equals space 1 space when space straight x space equals space straight x over 2

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 Multiple Choice QuestionsShort Answer Type

416.

The total cost C(x) associated with the production of x units of an item is given by C(x) = 0.005x3 - 0.02 x2 + 30 x +5000. Find the marginal cost when 3 units are produced, whereby marginal cost we mean the instantaneous rate of total cost at any level of output.


417.

Differentiate tan-1 1 + cos xsin x with respect x.


418.

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419.

Find the intervals in which the function f(x)  =  is

a) Strictly increasing

b) Strictly decreasing


420.

An open tank with a square base and vertical sides is to be constructed from a metal sheet so as to hold a given quantity of water. Show that the cost of material will be least when the depth of the tank is half of its width. If the cost is to be least when depth of the tank is half of its width. If the cost is to be borne by nearby settled lower income families, for whom water will be provided, what kind of value is hidden in this question?


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