tolong jawab no 18 besok di kumpulin

Kelas 7 Matematika
Bab Aljabar

(a + b)/(a - b) = 1/5
5 (a + b) = a - b
5a + 5b = a - b
5a - a = - b - 5b
4a = -6b
2a = -3b
a = -3b/2


(a² - b²)/(a² + b²)
= ((-3b/2)² - b²)/((-3b/2)² + b²)
= (9b²/4 - 4b²/4) / (9b²/4 + 4b²/4)
= (5b²/4) / (13b²/4)
= 5 : 13