Jawabanmu

2014-05-21T08:20:29+07:00
Panjang = 2x+4
lebar = 8-x
Panjang x lebar
= (2x+4) (8-x)
= 16x - 2x^2 + 32 - 4x
= -2x^2 + 16x-4x +32
= -2x^2 + 12 x + 32
= 2x^2 - 12 x - 32
= x^2 - 12x - 32
Nilai maksimum F' (x) = 0
F = 2x -12
 2x = 12
x = 12/2 = 6
Jadi lebar persegi panjang= (8-x) = 8-6 = 2 cm