Question

if 3x + y = 9 and 2 x - y = 11. what is the value of x? brainly
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Answer 1

Answer:

3x+y=9⟹y(3x+y)=y(9)⟹3xy+y2=9y

⟹3xy=9y−y2⟹xy=3y−13y2

In order to find the maximum value of x y we differentiate 3y−13y2

ddy(3y−13y2)=3−23y

For maximum value

3−23y=0⟹23y=3⟹y=92

∴(xy)max=3(92)−(13)×(92)2

=(272)−(274)

=(274)=6.75