Câu 14:
a: \(A=3x^2y\cdot4xy^3-6xyz^3+18x^5y^6:6x^2y^2\)
\(=12x^4y^4-6xyz^3+3x^3y^4\)
b: \(A-B=7x^3y^2-4xyz^3\)
=>\(B=12x^4y^4-6xyz^3+3x^3y^4-7x^3y^2+4xyz^3\)
=>\(B=12x^4y^4+3x^3y^4-7x^3y^2-2xyz^3\)
Câu 15:
a: \(2\left(x+5\right)-3x=7\)
=>2x+10-3x=7
=>10-x=7
=>x=10-7=3
b: \(\left(x-7\right)\left(x+3\right)-\left(x-1\right)\left(x+4\right)=-3\)
=>\(x^2+3x-7x-21-\left(x^2+4x-x-4\right)=-3\)
=>\(x^2-4x-21-x^2-3x+4=-3\)
=>-7x=-3+21-4=-7+21=14
=>x=-2
c: \(x^2-2x+1=25\)
=>\(\left(x-1\right)^2=25\)
=>\(\left[{}\begin{matrix}x-1=5\\x-1=-5\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=6\\x=-4\end{matrix}\right.\)
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