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[tex]f(x,y)=-x^2-y^2-10xy+4y-4x+2 [/tex]

we are meant to find and classify all local extrema. i got:

[tex]f_x=-2x-10y-4 [/tex] and [tex] f_y=-2y-10x+4[/tex]

i've never had two variables at this stage, and i can't solve for any of the points. the text doesn't seem to say anything about this...