Răspuns :
x²-85=(x-1)²
x²-85=x²-2x+1
-85=-2x+1
2x=85+1
x=86/2=43
verificare 43²-42²=1849-1764=85
x²-85=x²-2x+1
-85=-2x+1
2x=85+1
x=86/2=43
verificare 43²-42²=1849-1764=85
x la puterea -85=(x-1) la puterea
x la puterea -85=x la puterea -2x+1
-85=-2x+1
2x=85+1
x=86/2=43