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burhan101

  • 2 years ago

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

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

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

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

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

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

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

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

  8. burhan101
    • 2 years ago
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    think the answer key's wrong then ?

  9. dan815
    • 2 years ago
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    yes

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

  11. dan815
    • 2 years ago
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    graph it and ull know for sure

  12. dan815
    • 2 years ago
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    |dw:1371791477746:dw|

  13. xartaan
    • 2 years ago
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    1 Attachment
  14. dan815
    • 2 years ago
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    |dw:1371791538467:dw|

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

  16. dan815
    • 2 years ago
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    |dw:1371791697708:dw|

  17. dan815
    • 2 years ago
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    +22

  18. dan815
    • 2 years ago
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    |dw:1371791721412:dw|

  19. genius12
    • 2 years ago
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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 \(\bf (2,\infty)\)

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