Calculus help
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Question

Calculus help
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lochana · Answer

inflation are described with second derivatives

amy0799 · Answer

f'(x)=5cosx-sinx
f''(x)=-5sinx-cosx

lochana · Answer

exactly. now you can find solutions at f''(x) = 0

amy0799 · Answer

-5sinx-cosx=0
-5sinx=cosx
-5=sinx/cosx=tanx
is this correct? i got stuck on this part

lochana · Answer

so
-5sinx = cosx
tanx = $\frac{-1}{5}$

amy0799 · Answer

how did u get -1/5?

lochana · Answer

let me show you$$-5sinx = cosx\ \frac{-5sinx}{cosx} = \frac{cosx}{cosx} \ -5tanx = 1 \tanx = \frac{-1}{5}$$ right?

amy0799 · Answer

ooh ok, i understand now

lochana · Answer

yes. can you guess what two angles are they talking about?

lochana · Answer

they ask you two x values. smaller and larger

amy0799 · Answer

umm no, how do i figure out the angles?

lochana · Answer

there are two angles that gives -1/5 for tanx in [0,2pi]

lochana · Answer

do you know about 4 quadrants ?

lochana · Answer

|dw:1447602901721:dw|

lochana · Answer

here, tan values are always negative on 2nd quadrant and 4th quadrant

lochana · Answer

okay?

amy0799 · Answer

how do you know that?

lochana · Answer

lochana · Answer

|dw:1447603142688:dw|

lochana · Answer

can you tell me in which quadrants tangents are negative(-)?

amy0799 · Answer

2nd and 4th

lochana · Answer

yes. that's right. you better try to remember above picture. it is pretty valuable :)

lochana · Answer

so let me show you how to find those values from quadrants.
|dw:1447603381572:dw|

these x angles are our final solutions