(1-9x)²=0 ( aici ai formula de calcul prescurtat (a-b)²=a²-2ab+b² )
1-18x+81x²=0 ⇔ 81x²-18x+1
Obtii o ecuatie de gradul 2 si se aplica formula cu Δ=b²-4ac
Δ=18²-4·81 = 324-324= 0
Daca Δ=0 ecuatia are o singura solutie, adica x=-b/2a⇒x=-(-18)/2⇒x=18/2⇒x=9
