/sci/ - Science & Math

>>5607372
Differentiate the parabola at a.
You now have the slope of the tangent in terms of a.
You also know that (a,a^2+4) is on the line and (0,-3) is on the line which is enough to solve for a.

>>5607384
wait, I don't see how you can get the slope from that.

>>5607391
You don't understand how to get the slope from a derivative?

>>5607393
I'm supposed to take the derivative of that?

>>5607397
You are either trolling or seriously fucked if you're heading into a calc 1 exam not knowing that the slope of a tangent at a point is the derivative of the function at that point.

>>5607397
dude I think you should draw a diagram first
its better if you aren't spoonfed trust me

>>5607399
oh, okay I know that but it's just how like the problem is written... She usually indicates us like f'(x) and what not..

kk so I should do this:
1. graph
2. Find d / dx of y=x^2+4
3. Replace x by 0.
4. find equation of tangent line

did I screw up somewhere?

>>5607372
>>5607391

Differentiate from first principles

>>5607408
Seriously, draw a fucking picture.

>>5607401
is right.

But, since you're clearly wanting to be spoonfed I'll help you;
why are you replacing x with 0?
Is the line tangent to the curve at x=0?

>>5607416
f(x+h) - f(x)
--------------
h

I know that's an important one but I'm not 100% sure. It's the LONG form to find the derivative right?

oh this exam is going to be painful.


>>5607419
already drew it.

well the tangent line goes through (0,-3)

>>5607424
Way to not answer my question.
Does the line touch the graph when x=0?
Yes or no.

>>5607428
the tangent line, yes

>>5607432
I'm out.
Enjoy failing.

>>5607432
:|
Draw the pic bro, you'll understand

>>5607434
>>5607438

okay, this is the graph of y=x^2 +4.

The tangent line passes through (0,-3) but does not touch the point (0,0)

>>5607447
ok here's a hint

the two tangent lines intersect

there's an equation you can make out of that

If I tell you anymore solving this question will not benefit you, not more hints faggit

>>5607424 >I know that's an important one but I'm not 100% sure. It's the LONG form to find the derivative right?

It's not the long form, this is what you're actually wanting to do instead of just following miscellaneous steps.

>>5607462
not OP, but wondering how you find slope when you don't know where we're taking the tangent line of the graph at x = ?

>>5607462
They both intersect at (0,-3).
Just tell me if I'm on the right track :
I find f' (x).
The answer = m (the slope)

>>5607476
you use the derivative, d / dx
or
f(x+h)-f(x)
------------
h

>>5607485
f'(x) is defined as the slope of the tangent at that point, yes.

>>5607505
just one question,
what point do I take?
Usually it'd be the x1, this time it's 0.

do I really take f'(0).
That'd be equal to 0.
f (x) = x^2+4
f '(x) = 2x

sorry. I probably sound retarded as hell right now.

>>5607517
no hints fgt
re-read what i said

>>5607524
OH. OH.

delta y/x = x^2+4
?

if not, I'm going to call someone to get more help. I always ask online to not sound as dumb irl.

>>5607533
post what they tell you, this is killing me.
and thx for the help fuckers.

>>5607533
what does delta have to do with anything wtf
read >>5607462
come on man you can do it

>>5607540
if it doesn't click it doesn't click, bitch. sometimes you just need to be told what you're doing wrong.

>>5607540
well (y2-y1) / (x2-x1) no? that would be delta.

>>5607547
it isn't clicking at all and I'm pretty embarrassed right now...

>>5607547
well you could not insult me for one

>>5607550
you were called a bitch, get over it.

>>5607547
>>5607549
wait what the hell did OP just split into two people

>>5607550
he's got a point. He's been trying to help me from the start.
I'm the one who everyone should be insulting... haha.....


and no, he's a different me. I just changed my name to Math Failure.

>>5607554
damn I wish my friends went on 4chan

>>5607557
http://answers.yahoo.com/question/index?qid=20100722200751AAtG64P
here ya go, OP, fuck you holier than thou /sci/ losers

>>5607547
>if it doesn't click it doesn't click, bitch. sometimes you just need to be told what you're doing wrong.

You're not doing it right.

>>5607416

Do this. Step by step, know what you're doing then apply it to the problem asked. Once you figure out why the first principles equation looks like it does you will solve this easily.

You're spending entirely too much time asking questions instead of thinking about the problem

http://www.s-cool.co.uk/a-level/maths/differentiation/revise-it/introduction

>>5607569
>spoonfeeding

You fucking dumbass

>>5607571
>>5607561
i think that we can derive, i was getting confused on how to plug 2x in as a slope to an equation that contained x's. i don't know this guy it's just been a long time since i tool calc and it was killing me that i couldn't get this.

>>5607569
I never came across that one...

okay so, what I have right now is

f(x) = x^2 + 4
f'(x) = 2x

2 is the slope of y= mx+b ;(0,-3)

-3= 2(0)-b
-3= -b
b=3.
y=2x-3


>>5607578
I had already searched on Y!A - Just didn't come across this one.. lol

>>5607571
made me do 3 exercises to very that
>>5607416
is equal to d / dx

yahoo answers: 1
/sci/fags: suck fat dick

>>5607606
I don't know why everyone thinks I'm on Y!A.

I don't want spoon. I want to understand.

"Give a man a fish and you feed him for a day. Teach a man to fish and you feed him for a lifetime."

>>5607618
you have your slope for the tan line, m = 2x
you know it crosses the point (0,-3)
using slope-intercept for your tan line gives y = (2x)x - 3 or 2x^2 - 3
...

>>5607643
oh okay....
so .. I see...

so now I do
2x^2 -3 = x^2 + 4 ? to find the point, well the x.

>>5607651
yes, well when x = a, so really you're finding your a
answer courtesy of yahoo answers

>>5607651
>>5607657
I get
x= 7^0.5 /// x= sqrt(7)

aaaaaaaand that is .... CORRECT!!!!

>3 more problems
This week just won't end.

>>5607658
well done sir
bro five

>>5607662
*shameful bro five*


this is the second problem I don't understand.
what I understand :

Slope of f' (x) = -1
f' (x) = 30x^2

while trying to do so;
x= sqrt ( -1 / 30)
???

>People help out this guy for Calc 1 but when I asked a question about Diff EQ nobody helped out

Welp

>>5607679
what was your EQ?

was it >>5607476

>>5607683
Nah this was a few weeks ago

>>5607693
oh, /b/ and /sci/ always helped me whenever I asked them except a few times maybe.

>>5607679
>>5607683
if it is your question.
The first term = the "m", the slope.
per example:
in >>5607673

We know the slope of "y" but not of "f(x)";
y's slope must be equal to f(x)'s slope.

derive f(x) as such:
10x^3 + 60x^2 + 89x -90
30x^2 + 120x + 89

the slope of f(x) = 30x^2
the slope of y = -1x

>>5607694
your whole derivative is the slope of the tanget line, not just the first term

>>5607714
alrighty, Thanks!

I thought it was only first term so I was stuck.

so for my number ,

30x^2 + 120x +89 = -1x
?

>>5607720
no, the slope of the second line is just -1
remember y = mx +b, m is -1