jika luas persegi panjang 400cm². jika panjang persegi panjang 4× lebarnya . tentukanlah keliling persegi panjang tersebut!

luas = 400 cm²
panjang = 4l
lebar = l

luas = p x l
400 = 4l x l
400 = 4l²
400 : 4 = l²
100 = l²
√100 = l
10 cm = l

lebar = 10 cm
panjang = 4l = 4(10) = 40 cm

keliling = 2 (p+l)
             = 2 (40 +10)
             = 2 x 50 = 100 cm

L = p x l
= 4l x l = 400
= 4l² = 400
= l² = 400 : 4
= l² = 100
l = √100
l = 10 cm

p = 4L = 4 x 10 = 40 cm

K = 2 ( p+l )
K = 2 ( 40 + 10 )
K = 2 x 50
K = 100 cm