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Calculati:
a)(x-1)(x+2)+(3x-1)(2x+5)-3x(x+1)=
b)(x-7)(x+3)-(x+1)(x+2)+(5-x)(x-4)=
c)(a-b)(a+3b)+(2a-b)(a+2b)-(a+b)(a-2b)=
d)(2-x)(x+[tex] x^{2} [/tex])-[tex] x^{2} [/tex](3+x)+8+(x+2)(5+[tex] x^{2} [/tex])=