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a) \(A=\left(x-y\right)^2+\left(x+y\right)^2\)
\(=\left(x^2-2xy+y^2\right)+\left(x^2+2xy+y^2\right)\)
\(=x^2-2xy+y^2+x^2+2xy+y^2\)
\(=\left(x^2+x^2\right)-\left(2xy-2xy\right)+\left(y^2+y^2\right)\)
\(=2x^2+2y^2\)
\(=2.\left(x^2+y^2\right)\)
b) \(B=\left(2a+b\right)^2-\left(2a-b\right)^2\)
\(=\left(4a^2+4ab+b^2\right)-\left(4a^2-4ab+b^2\right)\)
\(=4a^2+4ab+b^2-4a^2+4ab-b^2\)
\(=\left(4a^2-4a^2\right)+\left(4ab+4ab\right)+\left(b^2-b^2\right)\)
\(=8ab\)\
c) \(C=\left(x+y\right)^2-\left(x-y\right)^2\)
\(=\left(x^2+2xy+y^2\right)-\left(x^2-2xy+y^2\right)\)
\(=x^2+2xy+y^2-x^2+2xy-y^2\)
\(=\left(x^2-x^2\right)+\left(2xy+2xy\right)+\left(y^2-y^2\right)\)
\(=4xy\)
d) \(D=\left(2x-1\right)^2-2\left(2x-3\right)^2+4\)
\(=\left(4x^2-4x+1\right)-2\left(4x^2-12x+9\right)+4\)
\(=4x^2-4x+1-8x^2+24x-18+4\)
\(=\left(4x^2-8x^2\right)-\left(4x-24x\right)+\left(1-18+4\right)\)
\(=-4x^2+20x-13\)
\(=-4x^2+20x-25+12\)
\(=-\left(4x^2-20x+25\right)-8\)
\(=-\left[\left(2x\right)^2-2.4x.5+5^2\right]-8\)
\(=-\left(2x-5\right)^2-8\)
Bài 1:
\(\left(2x+3\right)^2+\left(2x-3\right)^2+2\left(2x+3\right)\left(2x-3\right)\)
\(=\left(2x+3+2x-3\right)^2=\left(4x\right)^2=16x^2\)
Bài 2:
a, \(\left(x^2+xy+y^2\right)\left(x-y\right)+\left(x^2-xy+y^2\right)\left(x+y\right)\)
\(=x^3-y^3+x^3+y^3=2x^3\)
b, \(\left(2a-b\right)\left(4a^2+2ab+b^2\right)\)
\(=\left(2a\right)^3-b^3=8a^3-b^3\)
c, \(13x\left(3-x\right)-12\left(x+1\right)\)
\(=39x-13x^2-12x-12=-13x^2-27x-12\)
d, \(\left(2x-1\right)\left(x+12\right)\left(x^2+14\right)\)
\(=\left(2x^2+24x-x-12\right)\left(x^2+14\right)\)
\(=2x^4+23x^3-12x^2+28x^2+322x-168\)
\(=2x^4+23x^3+16x^2+322x-168\)
e, Giống câu b
Chúc bạn học tốt!!!