Toán Lớp 8: x^2-2xy-x^2+4y^2
x^2-6xy+9y^2-25z^2
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Toán Lớp 8: x^2-2xy-x^2+4y^2
x^2-6xy+9y^2-25z^2
Comments ( 2 )
$=-2xy+4y^2$
$=-2y(x-2y)$
* $x^2-6xy+9y^2-25z^2$
$=(x^2-6xy+9y^2)-25z^2$
$=(x^2-2.3xy+(3y)^2)-(5z)^2$
$=(x-3y)^2-(5z)^2$
$=(x-3y-5z)(x-3y+5z)$
Áp dụng HĐT số 2: $(A-B)^2= A^2-2AB+B^2$
HĐT số 3: $A^2-B^2=(A-B)(A+B)$