Keliling (2× + 48) lebar (12 - × ) agar luas nya maksimum maka panjangnya

Keliling = 2( p + l)
2x + 48 = 2 (p + (12 - x))
x + 24 =p + 12 - x
p = x + x + 24 -12
p = 2 x + 12

Rumus:
Keliling (K) = 2(p + l)

Diketahui:
K = (2x + 48)
l = (12 - x)

Ditanya:
p = ???

Jawab:
K = 2(p + l)
(2x + 48) = 2(p + 12 - x)
(2x + 48)/2 = p + 12 - x
x + 24 = p + 12 - x
p = x + 24 - 12 + x
p = 2x + 12