Calculus1 28 Online
OpenStudy (anonymous):

F(x)=2secx+tanx 0

OpenStudy (eyust707):

find the derivative?

OpenStudy (anonymous):

set it =0

OpenStudy (anonymous):

i know that... how do i find the derivatives.

OpenStudy (anonymous):

eyust707 take the derivative for her :0)

OpenStudy (eyust707):

okay

OpenStudy (eyust707):

you find the derivative of each term seprate

OpenStudy (eyust707):

lets look at the first term

OpenStudy (anonymous):

secx=secxtanx and tanx=secx^2. but what do you do with the 2 in front of the secx

OpenStudy (eyust707):

the two is a constant is just hangs out in front

OpenStudy (anonymous):

yup

OpenStudy (anonymous):

so, when finding derivatives it just stays? so the answer for the derivative would be 2secxtanx + secx^2?

OpenStudy (eyust707):

yep

OpenStudy (anonymous):

you don't have to use the product rule or whatever?

OpenStudy (eyust707):

product rule is when you there are two variable in the same term

OpenStudy (anonymous):

and 2 isn't a variable? ha. alright. got it.

OpenStudy (eyust707):

like tanxsecx would need product rule tanx+secx would not

OpenStudy (anonymous):

yeah i know. but the 2 is being multiplied...

OpenStudy (eyust707):

yea but the 2 is not a variable.. its a number

OpenStudy (anonymous):

but the derivative of a number is 0. that's what messes me up

OpenStudy (eyust707):

ahhh i see i see

OpenStudy (anonymous):

so it just hangs out there then. well that's dumb. ha

OpenStudy (eyust707):

yeah just like the derivative of 5*x^2

OpenStudy (anonymous):

is 10x

OpenStudy (anonymous):

oh got it. nice example.

OpenStudy (eyust707):

the five stays bring the two down you get 2*5x

OpenStudy (eyust707):

yep!

OpenStudy (anonymous):

so when you are finding the critical points...

OpenStudy (eyust707):

yes..

OpenStudy (anonymous):

you set it equal to zero... so it would be 0=2secxtanx+secx^2. bring the secx out?

OpenStudy (anonymous):

secx(2tanx+secx)?

OpenStudy (eyust707):

yea its been a little wile since i did that but your math is def correct

OpenStudy (anonymous):

good job brie

OpenStudy (anonymous):

I just don't get it. then you would have to set the inside of the parenthesis to zero... and i don't know how to do that.

OpenStudy (anonymous):

because they are two different trig terms.

OpenStudy (eyust707):

2tanx+secx=0

OpenStudy (anonymous):

yeah. and then what

OpenStudy (eyust707):

well lets see not 100 percent sure but..

OpenStudy (eyust707):

2tanx=-secx

OpenStudy (eyust707):

tanx=sinx/cosx and secx = 1/cosx

OpenStudy (anonymous):

brilliant! alright. thank you

OpenStudy (anonymous):

wait wait wait. still don't get it.

OpenStudy (anonymous):

2sinx/cosx+1/cosx=2sinx/cosx

OpenStudy (eyust707):

its been hella days since i did these alvin you got these down?

OpenStudy (anonymous):

eliminate one of the trig functions and leave x on one side i think

OpenStudy (anonymous):

yeah... ha. but which one can be eliminated?

OpenStudy (anonymous):

sinx+1/cosx

OpenStudy (eyust707):

2tanx+cosx=1

OpenStudy (eyust707):

2tanx=1-cosx

OpenStudy (anonymous):

i thought it equaled 0?

OpenStudy (eyust707):

i think theres a rule for 1-cosx??

OpenStudy (eyust707):

hehe i messed up

OpenStudy (anonymous):

2tanx+secx=0

OpenStudy (anonymous):

thought you took the derivative before?

OpenStudy (anonymous):

that is what we ended up with

OpenStudy (anonymous):

now we are trying to find the critical points.

OpenStudy (anonymous):

for the derivative we ended up with secx(2tanx+secx)=0

OpenStudy (eyust707):

lets start from where we were 2tanx=-secx 2tanx= -1/cosx 2tanxcosx= -1 tanxcosx=-1/2 sinxcosx/cosx=-1/2

OpenStudy (anonymous):

brilliant!

OpenStudy (eyust707):

sooo...

OpenStudy (anonymous):

so sinx=-1/2 and that's at 7pii/6

OpenStudy (anonymous):

and 11pii/6

OpenStudy (anonymous):

for the secx=0

OpenStudy (anonymous):

1/cosx=0?

OpenStudy (eyust707):

that DNE

OpenStudy (anonymous):

why?

OpenStudy (eyust707):

1 over what number gives you zero?

OpenStudy (anonymous):

because 1 doesn't equal 0 when you multiply both sides by cosx?

OpenStudy (eyust707):

is there any number you can put in?

OpenStudy (anonymous):

right.. got it. thank you.

OpenStudy (eyust707):

well infinity would work... butt cosx is never greater than 1

OpenStudy (eyust707):

kk i got a midterm in the mornin i gots to study for but if you got skype shoot me a message on there and id be glad to help. my name is exactly the same on there

OpenStudy (anonymous):

wait... did we mess up

OpenStudy (eyust707):

lol maybe

OpenStudy (anonymous):

ohh nvm haha. thank gosh

OpenStudy (anonymous):

thanks for all the help.

OpenStudy (eyust707):

welcome =)

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