I am asked to(adsbygoogle = window.adsbygoogle || []).push({}); find all local maximum and minimum points for the function,so, naturally, I had to find the critical points. However, in the back of my book (Calculus Early Transcendentals 6E, James Stewart)

f(x,y) = (1+xy)(x+y)the only critical points are (1,-1) (-1,1)(both of which are saddle pointsbutthat's not what's important).

My question is, what did I do wrong in my mathematics?I am getting two extra sets of critical pointsand I'm wondering: did the book forget to mention them as possible points or did I mess up during the calculations? Probably the latter but I checked my math twice, the second time on the board.

I took a picture of my math because it seemed so much easier. Hopefully my hand writing is legible and the picture is big enough.

My critical points are (1,-1) (-1,1) (-2/6, 10/6) (10/6, -2/6)

If the image is illegible please tell me and I will type it all out on text.

Thank you for reviewing my question, I greatly appreciate it.

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# Calculating Critical points for multivariable functions.

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