luas suatu persegi panjang 48 cm persegi jika panjang x + 3 cm dan lebar 2 x kurang 4 maka panjang diagonal persegi panjang adalah

Luas = p x l
48 = (x+3)(2x-4)
48 = 2x^2 - 4x + 6x -12
48 = 2x^2 + 2x - 12
2x^2 + 2x -12 - 48 = 0
2x^2 + 2x - 60 = 0 (bagi 2)
X^2 + x - 30 = 0
(x + 6) (x-5) = 0
X = - 6 (Tm)
X = 5

P= x +3 = 5 + 3 = 8
L = 2x - 4 = 2.5 - 4 = 10 - 4 = 6

Panjang diagonal = akar p^2 + l^2
= akar 8^2 + 6^2
= akar 64 + 36
= akar 100
= 10 cm