<s>[INST] What is the value of the expression $2x^2 + 3xy – 4y^2$ when $x = 2$ and $y = - 4$? What is the value of the expression $2x^2 + 3xy – 4y^2$ when $x = 2$ and $y = - 4$?
I'm not good at algebra so please explain in easy to understand steps.
Thanks
 [/INST] Subbing in $x=2$ and $y=-4$ into the equation gives: 
$2(2^2) +3(2)(-4)-4((-4)^2)=2(4) + (-24) -4(16)=8-24-64=8-88=-80$
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