<s>[INST] If $4x^2+y^2=40$ and $xy=-6$, find the value of $2x+y$. If $4x^2+y^2=40$ and $xy=-6$, find the value of $2x+y$.
I tried the following,
As we know, $(a+b)^2=a^2+b^2+2ab$
Therefore, $(4x^2+y^2)^2=(4x^2)^2+(y^2)+2(4x^2*y^2)$
$=16^4+y^4+8x^2y^2$
What should I do know? Please help. I am stuck.
 [/INST] Hint:
$(2x+y)^2-4xy=4x^2+y^2$
You can take it from here?
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