12. Efectuați calculele: a) (2-3x)²+(2+ 3x)²-(2x-3)²-(4x − 3)(4x + 3); b) (2r²+ y)²-(2r²- y)² + (x² + y)(x² −y); d) (2x + 5)²-(3x - 5)² + (2x-7)(2x + 7); 13. Efectuati calculele: c) (x+3)² + (x + 1)²-(2x + 1)(2x - 1); e) (x+4)²-(2x-3)(2x + 3) + (2x + 1)²​