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Bab Fungsi

L(x) = 9x - x^2
L = 20 m^2



P = X m
l = 9 - x

L = P × l
9x - x^2 = x * (9 - x)
9x - x^2 = 9x - x^2
20 = 9x - x^2
x^2 - 9x + 20 = 0
(X - 5) (X - 4) = 0
X = 5
X = 4

Dibuktikan :

L = 9x - x^2
L = 9(4) - 4^2
L = 36 - 16
L = 20 m^2

l = 9 - x
l = 9 - 4
l = 5 m

P = 4 m

Atau bisa juga

X = 5

L = 9x - x^2
L = 9(5) - 5^2
L = 45 - 25
L = 20 m^2

l = 9 - x
l = 9 - 5
l = 4 m

P = X
P = 5 m

(Terbukti)


Jadi panjangnya adalah 5 m

dik
: L(x) = 9x- x²

maka
L(x) = p*l
9x- x² = x (9- x) = 20 m²

maka
didapat
9x- x² = 20
x² - 9x + 20 = 0
( x - 5)(x-4) = 0
x = 5 V x= 4

Untuk x = 5
x(9-x) = 20
x = 5 (panjang)
l = 9-5 = 4 (lebar)

Untuk x= 4
4(9-4)
didapat
panjang = 4
lebar = 5


karena panjang > lebar maka

x = 5 <<< Jawaban