sebuah persegi panjan berukuran panjan (2x+1) cm dan lebar (x-1) cm.jika kelilingnya 40 cm,maka luasnya....

Keliling persegi panjang
= 2(p+l)

2((2x+1)+(x-1)) = 40
(2x+1)+(x-1) = 20
3x = 20
x = 20/3
x = 6⅔ cm = 20/3 cm

Luas = p x l
(2x+1)(x-1)
= 2x² + x - 2x - 1
= 2x² - x - 1
= 2(20/3)² + 20/3 - 1
= 2(400/9) + 20/3 - 1
= 800/9 + 20/3 - 1
= 800/9 + 60/9 - 1
= 740/9 - 1
= 82 2/9 - 1
= 81 2/9 cm²
= 81,22.... cm²

maaf kalo salah

k=2p+2l
40=2 (2x+1)+2 (x-1)
40=4x+2+2x-1
40=6x+1
6x=40-1
6x=39
x=39/6
x=6, 5
L=p×l
L=(2x+1)×(x-1)
L=(2.6, 5+1)×(6, 5-1)
L=(13+1)×5, 5
L=14×5, 5
L=77cm pangkat 2