Câu 1:
a,
$P= 3x^2y-xyz+2xyz-x^2z+4x^2z-3x^2y+4xyz-5x^2z-3xyz$
$= 2xyz-2x^2z$
Bậc: 3
b,
$P=2.(-1).2.3-2.(-1)^2.3$
$= -12-6=-18$
Câu 2:
a,
$f(x)= -5x^5+7x^3+x^2-2x+12$
$g(x)= -4x^4+x^3+7x^2+8x-9$
b,
$f(x)+g(x)= -5x^5-4x^4+8x^3+8x^2+6x+3$
$f(x)-g(x)= -5x^5-4x^4+6x^3-6x^2-10x+21$
$2f(x)-3g(x)= -10x^5+14x^3+2x^2-4x+24-(-12x^4+3x^3+21x^2+24x-27)$
$= -10x^5+12x^4+11x^3-19x^2-28x+51$