Toán Lớp 8: thực hiện phép tính
a, x(x-1) b,(x+3y)(x-3y+2)
c, (x+3)^2 d, (3x-2)(3x+2)-9x^2
cần gấpppppppppppp
camon!
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Toán Lớp 8: thực hiện phép tính
a, x(x-1) b,(x+3y)(x-3y+2)
c, (x+3)^2 d, (3x-2)(3x+2)-9x^2
cần gấpppppppppppp
camon!
Comments ( 2 )
b,(x+3y)(x-3y+2)=x^2-3xy+2x+3xy-9y^2+6y=x^2+2x-9y^2+6y
c, (x+3)^2 =x^2+2.3.x+3^2=x^2+6x+9
d, (3x-2)(3x+2)-9x^2=9x^2+6x-6x-4-9x^2=-4
$=x^2-x$
$=x^2-3xy+2x+3xy-9y^2+6y$
$=x^2+2x-9y^2+6y$
$=x^2+6x+9$
$=9x^2-4-9x^2$
$=-4$