Question

已知A=x^3-4ax^2+3ax-5,B=bx^2-2bx+10,A-B=x^3+20x^2-10x15,求A-B

求A+B，打错了

Answer 1

解
A-B
=(x³-4ax²铅陪+3ax-5)-(bx²-2bx+10)
=x³仔薯+(-4a-b)x²+(3a+2b)x-15
=x³槐戚蠢+20x²-10x-15
∴
-4a-b=20
3a+2b=-10
∴a=-6，b=4
∴a-b——求这个吧
=-6-4
=-10

追问

打错了，是A+B

追答

A-B
=(x³-4ax²+3ax-5)-(bx²-2bx+10)
=x³+(-4a-b)x²+(3a+2b)x-15
=x³+20x²-10x-15
∴
-4a-b=20
3a+2b=-10
∴a=-6，b=4
∴A+B
=(x³-4ax²+3ax-5)+(bx²-2bx+10)
=x³+(b-4a)x²+(3a-2b)x+5
=x³+28x²-26x+5