Find the intervals in which the following functions are strictl

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 Multiple Choice QuestionsShort Answer Type

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181.

Find the intervals in which the following functions are strictly increasing or strictly decreasing:
2x3 – 8x2 + 10x + 5


Let f (x) – 2x– 8x2 + 10x + 5
∴    f ' (x) = 6x2– 16x + 10 = 2 (3x2 – 8x + 5) = 2 (x – 1) (3x – 5)
For  f (x) to be increasing,
f ' (x) > 0 ⇒ 2 (x – 1) (3x – 5) > 0 ⇒ (x – 1) (3 x – 5) > 0
therefore space space space space either space straight x space less than 1 space space space space space space space or space space space straight x space space greater than space 5 over 3
space space space space therefore space space space straight f left parenthesis straight x right parenthesis space is space increasing space in space left parenthesis negative infinity comma space 1 right parenthesis space union space space space open parentheses 5 over 3 comma space infinity close parentheses space space space space space space space space
             For f(x) to be decreasing, 
         straight f apostrophe left parenthesis straight x right parenthesis space less than space 0 space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space space rightwards double arrow space space 2 space left parenthesis straight x minus 1 right parenthesis thin space left parenthesis 3 straight x minus 5 right parenthesis space less than space 0
rightwards double arrow space space space left parenthesis straight x minus 1 right parenthesis thin space left parenthesis 3 straight x minus 5 right parenthesis thin space less than 0 space space space space space space space space space rightwards double arrow space space 1 less than straight x less than 5 over 3
therefore space space space space straight f left parenthesis straight x right parenthesis space is space decreasing space in space 1 less than straight x less than 5 over 3
therefore space space space straight f left parenthesis straight x right parenthesis space is space decreasing space in space open parentheses 1 comma space 5 over 3 close parentheses

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182.

Find the intervals in which the following functions are strictly increasing or strictly decreasing:
2x3 – 6x2 – 48x + 17

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183.

Find the intervals in which the following functions are strictly increasing or strictly decreasing:
f (x) = 2x– 9x2 + 12x + 30

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184.

Find the intervals in which the following functions are strictly increasing or strictly decreasing:
f (x) = 2x3 – 3x2 – 36x + 7

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185.

Find the intervals in which the following functions are strictly increasing or strictly decreasing:
f(x) = 2x3 – 21x2 + 36x – 40 

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186.

Find the intervals in which the following functions are strictly increasing or strictly decreasing:
4x3 – 6x2 – 72x + 30

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187.

Find the intervals in which the following functions are strictly increasing or strictly decreasing:
– 2x3 – 9x2 – 12x + 1

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188.

Find the intervals in which the function
straight f left parenthesis straight x right parenthesis space equals space fraction numerator 4 straight x squared plus 1 over denominator straight x end fraction comma space space straight x not equal to 0, is
(a) increasing (b) decreasing.

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 Multiple Choice QuestionsLong Answer Type

189.

Find the intervals in which the function f is given by 
straight f left parenthesis straight x right parenthesis space equals space straight x cubed plus 1 over straight x cubed comma space space space straight x not equal to 0 space space is space
(i) increasing    (ii) decreasing

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190.

Determine for which values of x, the function f (x) = x4 – 2x2 is increasing or decreasing.

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