SE DA a/b=5/2⇒ 2a=5b ⇒ a=5b/2
inlocuim pe a in relatia ce trebuie demonstrata si vedem daca verifica egalitatea
4(5b/2)²+25b²=20b(5b/2)
4(25b²/4)+25b²=50b² - aduce la acelasi numitor comun⇒
100b²+100b²=200b²
200b²=200b²
am verificat egalitatea
dar 4a²-20ab+25b²=0⇒ aplicam formula (a-b)²=a²-2ab+b²⇒
(2a-5b)²=0⇒2a-5b=0⇒2a=5b⇒a/b=5/2
