Find the intervals in which the function  is increasing or dec

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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

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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.


Here,  straight f left parenthesis straight x right parenthesis space equals space straight x over 2 plus 2 over straight x comma space space space space space straight x not equal to space 0
therefore space space space space straight f apostrophe left parenthesis straight x right parenthesis space equals space 1 half minus 2 over straight x squared space equals space fraction numerator straight x squared minus 4 over denominator 2 straight x squared end fraction space equals space fraction numerator left parenthesis straight x minus 2 right parenthesis thin space left parenthesis straight x plus 2 right parenthesis over denominator 2 straight x squared end fraction

(i) For f(x) to be increasing,  straight f apostrophe left parenthesis straight x right parenthesis space greater than space 0
therefore space space space space space fraction numerator left parenthesis straight x minus 2 right parenthesis thin space left parenthesis straight x plus 2 right parenthesis over denominator 2 straight x squared end fraction greater than 0 space space space space space space space space space space rightwards double arrow space space space space left parenthesis straight x minus 2 right parenthesis thin space left parenthesis straight x plus 2 right parenthesis thin space greater than space 0
rightwards double arrow space space space space space space either space straight x space less than negative 2 space space space space space space space space space space space space space or space space space space straight x space greater than space 2
therefore space space space space space space space straight f left parenthesis straight x right parenthesis space is space increasing space for space straight x space greater than 2 space space space or space space straight x space less than space minus space 2.

(ii) For f(x) to be decreasing, straight f apostrophe left parenthesis straight x right parenthesis space less than space 0
therefore space space space space space space fraction numerator left parenthesis straight x minus 2 right parenthesis thin space left parenthesis straight x plus 2 right parenthesis over denominator 2 straight x squared end fraction less than 0 space space space space space space space space space space space rightwards double arrow space space space space left parenthesis straight x minus 2 right parenthesis thin space left parenthesis straight x plus 2 right parenthesis thin space less than 0
rightwards double arrow space space space space minus 2 less than straight x less than 2
therefore space space space straight f left parenthesis straight x right parenthesis space decreases space for space minus 2 less than straight x less than 2.
   

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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

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).

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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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