Hello!

I have a question I'm struggling with, my last question was answered so helpfully I thought I'd try my others out here! Especially since my exam is in less than 3 hours!

Its a 'Two variable function Extrema' question

Q: The gravitational attraction at the point (x,y)=(1/x)+(4/y)+(9/(4-x-y))

Prove that G(x,y) has a maximum value of 9

These type of questions always stump me, sorry.

Thanks for any aid