anonymous
  • anonymous
Determine the derivative, all the critical numbers and the intervals of increase and decrease y=-5x²+20x+2
Mathematics
  • Stacey Warren - Expert brainly.com
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SOLVED
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jamiebookeater
  • jamiebookeater
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anonymous
  • anonymous
\[\huge y'=-10x+20\] \[\huge 0=-10x+20\] \[x=2\]
anonymous
  • anonymous
i get : intervals of increase x<2 intervals of decrease x>2 but the answer key says the opposite
anonymous
  • anonymous
when \[y \prime >0, \] then increasing.

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More answers

anonymous
  • anonymous
what's in intervals of increase / decrease tho?
anonymous
  • anonymous
I got the same answer as you @burhan101 intervals of increase x<2 intervals of decrease x>2
anonymous
  • anonymous
x>2 it decreases x<2 it increases.
johnweldon1993
  • johnweldon1993
Right...I as well @koymoi ...I think maybe your answer key is wrong @burhan101
anonymous
  • anonymous
think the answer key's wrong then ?
dan815
  • dan815
yes
anonymous
  • anonymous
yeah, i thought it was a fairly straight forward question
dan815
  • dan815
graph it and ull know for sure
dan815
  • dan815
|dw:1371791477746:dw|
anonymous
  • anonymous
1 Attachment
dan815
  • dan815
|dw:1371791538467:dw|
dan815
  • dan815
oh oops that shud be + when i multiplied by -5
dan815
  • dan815
|dw:1371791697708:dw|
dan815
  • dan815
+22
dan815
  • dan815
|dw:1371791721412:dw|
anonymous
  • anonymous
@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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