Let f be a function defined on [a, b] such that f ' (x) > 0,

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 Multiple Choice QuestionsLong Answer Type

191.

Find intervals in which the function given by 
straight f left parenthesis straight x right parenthesis space equals space 3 over 10 straight x to the power of 4 minus 4 over 5 straight x cubed minus 3 straight x squared plus 36 over 5 straight x plus 11
is (a) strictly increasing (b) strictly decreasing.

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 Multiple Choice QuestionsShort Answer Type

192.

Find the intervals in which the function straight f left parenthesis straight x right parenthesis space equals space straight x over 2 plus 2 over straight x is increasing or decreasing.

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193.

Separate open square brackets 0 comma space space space straight pi over 2 close square brackets into sub-intervals in which the function f (x) = sin 3x is increasing or decreasing.

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 Multiple Choice QuestionsLong Answer Type

194.

Find the intervals in which the following function is increasing or decreasing:
f (x) = sinx – cosx, 0 < x < 2straight pi

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 Multiple Choice QuestionsShort Answer Type

195. Find the intervals in which the following function is increasing or decreasing:
straight f left parenthesis straight x right parenthesis space equals space log space left parenthesis 1 plus straight x right parenthesis space minus space fraction numerator straight x over denominator 1 plus straight x end fraction


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196.

Find the intervals in which the following function is increasing or decreasing
f (x) = (x + 2) e–x 

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 Multiple Choice QuestionsLong Answer Type

197. Find the intervals in which the function f given by 
f (x) = sin x + cos x. 0 ≤ a ≤ 2 straight pi is increasing or decreasing.

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198.

Find the intervals in which the function (x + 1)3 (x – 1)3 is strictly increasing or decreasing.

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 Multiple Choice QuestionsShort Answer Type

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199.

Let f be a function defined on [a, b] such that f ' (x) > 0, for all x ∊ (a, b). Then prove that f is strictly increasing function of (a, b).


Since f '(x) > 0 in (a, b).
therefore space space space space space for space any space straight c space element of space space left parenthesis straight a comma space straight b right parenthesis comma space straight f apostrophe left parenthesis straight c right parenthesis space greater than space 0
By Lagrange's mean value theorem,
                  straight f apostrophe left parenthesis straight c right parenthesis space equals space fraction numerator straight f left parenthesis straight x subscript 2 right parenthesis minus straight f left parenthesis straight x subscript 1 right parenthesis over denominator straight x subscript 2 minus straight x subscript 1 end fraction space where space straight a less than straight x subscript 1 less than straight c less than straight x subscript 2 less than straight b
But straight f space apostrophe space left parenthesis straight c right parenthesis space greater than space 0                                                                           open square brackets because space space space of space left parenthesis 1 right parenthesis close square brackets
therefore space space space space space space fraction numerator straight f left parenthesis straight x subscript 2 right parenthesis space minus straight f left parenthesis straight x subscript 1 right parenthesis over denominator straight x subscript 2 minus straight x subscript 1 end fraction greater than 0
rightwards double arrow space space space space straight f left parenthesis straight x subscript 2 right parenthesis space minus straight f left parenthesis straight x subscript 1 right parenthesis thin space greater than 0
rightwards double arrow space space space space straight f left parenthesis straight x subscript 2 right parenthesis thin space greater than space straight f left parenthesis straight x subscript 1 right parenthesis space space space space rightwards double arrow space space space straight f left parenthesis straight x subscript 1 right parenthesis thin space less than space space straight f left parenthesis straight x subscript 2 right parenthesis
therefore space space space space space space straight x subscript 1 space less than space straight x subscript 2 space space space space space space rightwards double arrow space space space space straight f left parenthesis straight x subscript 1 right parenthesis thin space less than space straight f left parenthesis straight x subscript 2 right parenthesis space for all space straight x subscript 1 comma space space straight x subscript 2 space element of space left parenthesis straight a comma space straight b right parenthesis
therefore space space space straight f left parenthesis straight x right parenthesis space is space strictly space increasing space in space left parenthesis straight a comma space straight b right parenthesis

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200.

On which of the following intervals is the function f given by f (x) = x100 + sin x – 1 strictly decreasing?
(A)   (0, 1)     (B) open parentheses straight pi over 2 comma space straight pi close parentheses      (C)  open parentheses 0 comma space straight pi over 2 close parentheses    (D) None of these 

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