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[latex]#7) \\a) (2x+y)(3x-2y)-(3x+2y)(2x-y)+8x(y-1)=\\=6x^2-4xy+3xy-2y^2-(6x^2-3xy+4xy-2y^2)+8xy-8x=\\=6x^2-4xy+3xy-2y^2-6x^2+3xy-4xy+2y^2+8xy-8x=\\=6xy-8x=2x(3y-4)\\\\b) (7s-d)(2u+3)-(2s-3)(7u-1)-u(21-2d)=\\=14su+21s-2du-3d-14su+2s+21u-3-21u+2du=\\=23s-3d-3\\\\v) (11g-2f)(2f+g)+(11g+2f)(2f-g)-40fg=\\=22fg+11g^2-4f^2-2fg+22fg-11g^2+4f^2-2fg-40fg=\\=0\\ \\ [/latex] [latex]g) \frac1{264}(12a+11b)(11a+12b)+\frac1{264}(12a-11b)(11a-12b)=\\\\= \frac1{264}(132a^2+144ab+121ab+132b^2)+\frac1{264}(132a^2-\\-144ab-121ab+132b^2)=\\\\= \frac1{264}(132a^2+265ab+132b^2)+\frac1{264}(132a^2-265ab+132b^2)=\\\\= \frac1{264}(132a^2+265ab+132b^2+132a^2-265ab+132b^2)=\\\\=\frac1{264}(264a^2+264b^2)=\frac{264}{264}(a^2+b^2)=a^2+b^2[/latex]