Q: find the coordinates of the two stationary points on the curve with equation
x^2 + 4xy+2y^2 +18
what I've done so far:
differentiation of 4xy (product rule)
v=4x
u= y
dv/dx = 4
du/dx = dy/dx
dy/dx = 4x.dy/dx + 4y
then differentiated the rest to get
dy/dx = 2x +4.dy/dx +4y + 4y.dy/dx
simplifiy = 2x + dy/dx(4y+4) + 4y
=2x + 4y + 4(dy/dx)(y+1)
looking for stationary points so dy/dx = 0
so
0 = (-2x-4y)/4(y+1)
the part I'm stuck on :
do do I say y = -1
and try and sub it into the original equation to get my x values ?