Помогите с алгеброй 7 класс:
1) (2a+b+c)2-(a-2b+c)2-3a2-3b2+8ab+2ac+6bc
2) [tex] (\frac{x+y}{2})^{2} - (\frac{x-y}{2})^{2} -xy[/tex]
1) (2a+b+c)2-(a-2b+c)2-3a2-3b2+8ab+2ac+6bc
2) [tex] (\frac{x+y}{2})^{2} - (\frac{x-y}{2})^{2} -xy[/tex]
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=((2a+b+c)+(a-2b+c))(2a+b+c)-(a-2b+c))-3a²-3b²+8ab+2ac+6bc=
=(2a+b+c+a-2b+c)(2a+b+c-a+2b-c)-3a²-3b²+8ab+2ac+6bc=
=(3a-b+2c)(a+3b)-3a²-3b²+8ab+2ac+6bc=
=3a²+9ab-ab-3b²+2ac+6bc-3a²-3b²+8ab+2ac+6bc=
=16ab-6b²+4ac+12bc