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(3x+2y+1) totul la a doua

Răspuns :

(a+b+c)^2= a^2 + b^2 + c^2 + 2ab + 2bc + 2ac
deci
(3x+2y+1)^2= (3x)^2 + (2y)^2 + 1^2 + 2*3x*2y + 2*2y*1 + 2*3x*1
= 9x^2 + 4y^2 + 1 + 12xy + 4y + 6x