f = x^2 + y^2 + Z^2 + lamda (ax + by + cz -d) = 0
F (patial y) = 2y + lamda * b
F (patial z) = 2z + lamda * c
Euler: d/dx F (partial y') - F (partial y) = 0 => 2y + lamda * b = 0
d/dx F (partial z') - F (partial z) = 0 => 2z + lamda * c = 0
Then I'd get y and z...
I know this is incorrect . Please help.