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burhan101

Determine the derivative, all the critical numbers and the intervals of increase and decrease y=-5x²+20x+2

  • 10 months ago
  • 10 months ago

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  1. burhan101
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    \[\huge y'=-10x+20\] \[\huge 0=-10x+20\] \[x=2\]

    • 10 months ago
  2. burhan101
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    i get : intervals of increase x<2 intervals of decrease x>2 but the answer key says the opposite

    • 10 months ago
  3. Abhishek619
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    when \[y \prime >0, \] then increasing.

    • 10 months ago
  4. burhan101
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    what's in intervals of increase / decrease tho?

    • 10 months ago
  5. koymoi
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    I got the same answer as you @burhan101 intervals of increase x<2 intervals of decrease x>2

    • 10 months ago
  6. Abhishek619
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    x>2 it decreases x<2 it increases.

    • 10 months ago
  7. johnweldon1993
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    Right...I as well @koymoi ...I think maybe your answer key is wrong @burhan101

    • 10 months ago
  8. burhan101
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    think the answer key's wrong then ?

    • 10 months ago
  9. dan815
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    yes

    • 10 months ago
  10. burhan101
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    yeah, i thought it was a fairly straight forward question

    • 10 months ago
  11. dan815
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    graph it and ull know for sure

    • 10 months ago
  12. dan815
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    |dw:1371791477746:dw|

    • 10 months ago
  13. xartaan
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    • 10 months ago
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  14. dan815
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    |dw:1371791538467:dw|

    • 10 months ago
  15. dan815
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    oh oops that shud be + when i multiplied by -5

    • 10 months ago
  16. dan815
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    |dw:1371791697708:dw|

    • 10 months ago
  17. dan815
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    +22

    • 10 months ago
  18. dan815
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    |dw:1371791721412:dw|

    • 10 months ago
  19. genius12
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    @burhan101 u don't need calculus to find intervals of increase/decrease. This is a parabola with a negative leading coefficient so it opens down. Using -b/2a we get -b/2a = 2, which is the x-coordinate of the vertex of the parabola. Since it opens down, function is increasing on \(\bf (-\infty,2)\) and decreasing on \(\bf (2,\infty)\)

    • 10 months ago
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