Câu hỏi của Duonp Thy

Question

Rút gọn biểu thức:
A = (2x + y)2 + (2x - y)2  + (4x2 - y2) + 3y
B = (x - 2) (x + 2) - (x + 2)2
C = (3x - 4y)2 + (3x - 4y)2

GV Nguyễn Trần Thành Đạt · Accepted Answer

$A=\left(2x+y\right)^2+\left(2x-y\right)^2+\left(4x^2-y^2\right)+3y\
=\left(4x^2+4xy+y^2\right)+\left(4x^2-4xy+y^2\right)+\left(4x^2-y^2\right)+3y\
=4x^2+4x^2+4x^2+4xy-4xy+y^2+y^2-y^2+3y=12x^2+3y-y^2\
B=\left(x-2\right)\left(x+2\right)-\left(x+2\right)^2\
=\left(x+2\right)\left(x-2-x-2\right)=-4\left(x+2\right)=-4x-8\
C=\left(3x-4y\right)^2+\left(3x-4y\right)^2\
=\left(9x^2-24xy+16y^2\right)+\left(9x^2-24xy+16y^2\right)\
=18x^2-48xy+32y^2$Câu trả lời: $A=\left(2x+y\right)^2+\left(2x-y\right)^2+\left(4x^2-y^2\right)+3y\
=\left(4x^2+4xy+y^2\right)+\left(4x^2-4xy+y^2\right)+\left(4x^2-y^2\right)+3y\
=4x^2+4x^2+4x^2+4xy-4xy+y^2+y^2-y^2+3y=12x^2+3y-y^2\
B=\left(x-2\right)\left(x+2\right)-\left(x+2\right)^2\
=\left(x+2\right)\left(x-2-x-2\right)=-4\left(x+2\right)=-4x-8\
C=\left(3x-4y\right)^2+\left(3x-4y\right)^2\
=\left(9x^2-24xy+16y^2\right)+\left(9x^2-24xy+16y^2\right)\
=18x^2-48xy+32y^2$

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