问题
选择题
设a，b，c满足abc≠0，a+b=c，则
|
答案
∵a+b=c，
∴a-c=-b，c-b=a，
则
| b2+c2-a2 |
| 2bc |
| a2+b2-c2 |
| 2ab |
=
| b2-a2+c2 |
| 2bc |
| a2-c2+b2 |
| 2ab |
=
| (b+a)(b-a)+c2 |
| 2bc |
| (a+c)(a-c)+b2 |
| 2ab |
=
| c(b-a)+c2 |
| 2bc |
| -b(a+c)+b2 |
| 2ab |
=
| b-a+c |
| 2b |
| -a-c+b |
| 2a |
=
| b-(a-c) |
| 2b |
| -a-(c-b) |
| 2a |
=
| b-(-b) |
| 2b |
| -a-a |
| 2a |
=1+（-1）=0．
故选A．