a) M + N = (6x2y + 8x + 7xy) + (5x2y + 7x + 3xy + 2)
= 6x2x + 8x + 7xy + 5x2y + 7x + 3xy + 2
= (6x2y + 5x2y) + (8x + 7x) + (7xy + 3xy) + 2
= 11x2y + 15x + 10xy + 2
M - N = (6x2y + 8x + 7xy) - (5x2y + 7x + 3xy + 2)
= 6x2y + 8x + 7xy - 5x2y - 7x - 3xy - 2
= (6x2y - 5x2y) + (8x - 7x) + (7xy - 3xy) - 2
= x2y + x + 7xy - 2
b) Sắp xếp : x4 + 2x3 + 3x2 - 5x
F(1) = 14 + 2.13 + 3.12 - 5.1
= 1 + 2 + 3 - 5
= 1
\(M+N\)
\(=\left(6x^2y+8x+7xy\right)+\left(5x^2y+7x+3xy+2\right)\)
\(=6x^2y+8x+7xy+5x^2y+7x+3xy+2\)
\(=\left(6x^2y+5x^2y\right)+\left(8x+7x\right)+\left(7xy+3xy\right)+2\)
\(=11x^2y+15x+10xy+2\)
\(M-N\)
\(=\left(6x^2y+8x+7xy\right)-\left(5x^2y+7x+3xy+2\right)\)
\(=6x^2y+8x+7xy-5x^2y-7x-3xy-2\)
\(=\left(6x^2y-5x^2y\right)+\left(8x-7x\right)+\left(7xy-3xy\right)-2\)
\(=x^2y+x+4xy-2\)
\(F\left(x\right)=3x^2+2x^3-5x+x^4\)
\(F\left(x\right)=x^4+2x^3+3x^2-5x\) ( sắp xếp )
\(F\left(1\right)=1^4+2.1^3+3.1^2-5.1\)( tính F(1) )
\(F\left(1\right)=1+2+3-5\)
\(F\left(1\right)=1\)
Vậy giá trị biể thức F(1) tại x = 1 là 1