Question

已知A=2a^2+3ab-2a-1,B=-2a^2+2ab+2b^2,求(1)A+B(2)A-B(3)A-1/2B

Answer 1

解：∵A=2a²+3ab-2a-1
　　B=-2a²+2ab+2b²
　(1)A+B
　　=2a²+3ab-2a-1+(-2a²+2ab+2b²)
　　=2a²+3ab-2a-1-2a²+2ab+2b²
　　=2b²+5ab-2a-1
　(2)A-B
　　=2a²+3ab-2a-1-(-2a²+2ab+2b²)
　　=2a²+3ab-2a-1+2a²-2ab-2b²
　　=4a²+ab-2a-2b²-1
　(3)A-1/2B
　　=2a²+3ab-2a-1-(1/2)(-2a²+2ab+2b²)
　　=2a²+3ab-2a-1+a²-ab-b²
　　=3a²+2ab-2a-b²-1

Answer 2

解：∵A=2a^2+3ab-2a-1，B=-2a^2+2ab+2b^2；
∴A+B=2a^2+3ab-2a-1-2a^2+2ab+2b^2
=5ab+2b^2-2a-1
A-B=2a^2+3ab-2a-1+2a^2-2ab-2b^2
=4a^2+ab-2b^2-2a-1
A-1/2B=2a^2+3ab-2a-1-1/2(-2a^2+2ab+2b^2)

Answer 3

A+B
=2a^2+3ab-2a-1-2a^2+2ab+2b^2
=5ab-2a-1+2b^2

A-B=
=2a^2+3ab-2a-1+2a^2-2ab-2b^2

=4a^2+ab-2a-1-2b^2

A-1/2B
=2a^2+3ab-2a-1+a^2-ab-b^2

=3a^2+2ab-2a-1-b^2

Answer 4

A+B=5ab-2a+2b^2-1
A-B=4a^2+ab-2a-2b^2-1