➡1⬅
a) 5x+15=5(x+3)
b) 9x²-25y²=(3x)²-(5y)²=(3x-5y)(2x+5)
c)x²+6x+5=(x²+2x+1)+(4x+4)=(x+1)²+4(x+1)=(x+1)(x+1+4)=(x+1)(x+5)
➡3⬅
a=(x+2)(x-3)+3x+7=x²-3x+2x-6+3x+7=x²+2x+1=(x+1)²
(x+1)²-patrat perfect
➡4⬅
x-1/x=4
x-1=4x
x-4x=1
-3x=1
x=-1/3
(-1/3)²+1/(-1/3)²=1/9+1supra1/9=10/9supra1/9=10•9/9=10