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(x + 1)² – (x - 2)² = 9;​

Răspuns :

(x + 1)² – (x - 2)² = 9

x²+2x+1-(x²-4x+4)=9

x²+2x+1-x²+4x-4=9

6x-3=9

6x=12

x=2