3:
a: \(M+5x^2-2xy=6x^2+9xy-y^2\)
=>\(M=6x^2+9xy-y^2-5x^2+2xy\)
=>\(M=x^2+11xy-y^2\)
b: \(N-\left(5y^2-xyz\right)=xy+2y^2-3xyz+4\)
=>\(N=xy+2y^2-3xyz+4+5y^2-xyz\)
=>\(N=7y^2+xy-4xyz+4\)
5:
a: \(A=1,5x^3y^2-3xyz+2x^2y-1,5x^3y^2+xy^2z+2,5xyz\)
\(=\left(1.5x^3y^2-1.5x^3y^2\right)+\left(-3xyz+2.5xyz\right)+2x^2y+xy^2z\)
\(=-0.5xyz+2x^2y+xy^2z\)
Khi x=y=-2 và z=3 thì \(A=-0.5\cdot\left(-2\right)\cdot\left(-2\right)\cdot3+2\cdot\left(-2\right)^2\cdot\left(-2\right)+\left(-2\right)\cdot\left(-2\right)^2\cdot3\)
\(=-0.5\cdot4\cdot3+2\cdot4\cdot\left(-2\right)-6\cdot4\)
\(=-6-24-16=-46\)
2: \(B=5x^2-2xy+y^2-x^2-y^2-4x^2+5xy-1\)
\(=3xy-1\)
Khi x=1,2 và y=5 thì B=3*1,2*5-1
=15*1,2-1
=18-1
=17
3:
\(C=x^2-xy^2+x^2y-y^2-x^2+y^2\)
\(=-xy^2+x^2y\)
Khi x=2 và y=0,5 thì \(C=-2\cdot0.5^2+2^2\cdot0.5\)
\(=-2\cdot0.25+4\cdot0.5\)
\(=-0.5+2=1.5\)
