printed area = 50 = xy
paper size, P(x)
= (x + 2*2)(y + 2*4)
=(x + 4)(y + 8)
= xy + 4y + 8x + 32
= 8x + 4(50/x) + (50 + 32)
= 8x + 200/x + 82
P'(x) = 8 - 200/x^2 = 0
x = √(200/8) = 5 (for x > 0)
answer : paper dimension = 9 x 18
:)
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