# implicite differenciation to find slope of curve at apoint

2 views (last 30 days)
sita on 3 Feb 2015
Answered: Mischa Kim on 7 Sep 2016
Hi,
I would like to do some thing like
x^2+y^2=1
d(x^2+y^2)/dx=d(1)/dx
d(x^2)/dx+d(y^2)/dx=0
2x+2y*dy/dx=0
dy/dx=-x/y
but
syms x y
f=x^2+y^2-1
diff(f,x,y)gives
2y
Thanks,
Sita
Sung Won Kim on 18 Aug 2016
Edited: Sung Won Kim on 18 Aug 2016
It would be better, If you use this When you defining f f=x^2+y^2==1
and I recommend to use syms x y(x) when you defining syms.
last, it is also necessary that diff(f,x) is used to differenciate the f by x (You don't need 'y')
then I think it will give an ans.
good luck
Kim

Mischa Kim on 7 Sep 2016
syms x y(x) f(x,y)
f = x^2+y^2-1 == 0;
df = diff(f,x)

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