4:
a: \(A=2xy\cdot x^3y^2\)
\(=2\cdot x\cdot x^3\cdot y\cdot y^2=2x^4y^3\)
b: \(B=\dfrac{1}{3}x^2yz\cdot x^2y^2\)
\(=\dfrac{1}{3}\cdot x^2\cdot x^2\cdot y\cdot y^2\cdot z=\dfrac{1}{3}x^4y^3z\)
c: \(C=-6\cdot xyz\cdot yz^2\)
\(=-6\cdot x\cdot y\cdot y\cdot z\cdot z^2=-6xy^2z^3\)
11:
a: \(9x^2+12x+4=\left(3x\right)^2+2\cdot3x\cdot2+2^2=\left(3x+2\right)^2\)
b: \(121y^2-110y+25\)
\(=\left(11y\right)^2-2\cdot11y\cdot5+5^2\)
\(=\left(11y-5\right)^2\)
8:
a: A+B
\(=x^5+3x^2y^2-5xy-8+x^5-3x^2y^2+3xy+1\)
\(=2x^5-2xy-7\)
b: A-B
\(=x^5+3x^2y^2-5xy-8-x^5+3x^2y^2-3xy-1\)
\(=6x^2y^2-8xy-9\)
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