A-Level Maths Question Differentiation help

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annonymous2394
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A curve has the equation y=ln3x-e^-2x. Show that the equation of the tangent at the point with an X coordinate of 1 is: y=[(e^2 2)/e^2]x - [(e^2 3)/e^2] ln3I've differentiated and got gradient as (2/e^2) 1... where do I go from here as curve doesnt cross y-axis so cant use y=mx c and can't use y-y1=m(x-x1) because I dont have any y co-ords ? Any help would be great thanks
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CaptainDuckie
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How can you find y coordinate if x is 1?
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Export kid
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Sub in x=1 to the original eqn to get a y coordinate
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annonymous2394
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(Original post by Export kid)
Sub in x=1 to the original eqn to get a y coordinate
(Original post by CaptainDuckie)
How can you find y coordinate if x is 1?
Thanks for replies but answer i get is off what Im trying to prove.. I've attached some photos so u know where I'm at
Last edited by annonymous2394; 4 weeks ago
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CaptainDuckie
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(Original post by annonymous2394)
Thanks for replies but answer i get is off what Im trying to prove.. I've attached some photos so u know where I'm at
Ok so you found the gradient

So what now
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DFranklin
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When x = 1, mx+c=m+c. Compare with the value of y when x = 1 to find c and rearrange to get it in the same form as the question is asking for.

You should not use a calculator during this question btw.
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annonymous2394
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Thanks for the help !

I've now got y=((2/e^2)+ 1)x - ((e/e^2 )+1 ) + ln3

its close but somehow need to add the 1 in the brackets to the 2/e^2 bit ? so that it looks the same as what im trying to prove

(this is the bit I was confused about at the start when I first got the gradient as its not the same )?
Attached files
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DFranklin
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To add the 1 in the first bracket, rewrite 1 as e^2 / e^2
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annonymous2394
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(Original post by DFranklin)
To add the 1 in the first bracket, rewrite 1 as e^2 / e^2
Thats what i initially thought but doesnt that make the bottom of the fraction 2e^2 instead of just e^2
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annonymous2394
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(Original post by annonymous2394)
Thats what i initially thought but doesnt that make the bottom of the fraction 2e^2 instead of just e^2
wait i am an idiot
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annonymous2394
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(Original post by annonymous2394)
wait i am an idiot
lol that was dumb of me I get it now thanks for the help have a good day
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CaptainDuckie
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(Original post by annonymous2394)
wait i am an idiot
(Original post by annonymous2394)
lol cant believe it that was dumb of me I get it now thanks for the help have a good day
Dont feel this way.

It’s normal to get things wrong.
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annonymous2394
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(Original post by CaptainDuckie)
Dont feel this way.

It’s normal to get things wrong.
hahaha no i know I find it quite funny just wasn't thinking properly!
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CaptainDuckie
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(Original post by annonymous2394)
hahaha no i know I find it quite funny just wasn't thinking properly!
Take your time
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