∴b2+c2-a2=bc,
∴
| b2+c2−a2 |
| 2bc |
| 1 |
| 2 |
∴cosA=
| 1 |
| 2 |
又A是三角形的内角,故A=
| π |
| 3 |
(2)∵2sin2
| B |
| 2 |
| C |
| 2 |
∴1-cosB+1-cosC=1∴cosB+cosC=1,
由(1)的结论知,A=
| π |
| 3 |
| 2π |
| 3 |
∴cosB+cos(
| 2π |
| 3 |
即cosB+cos
| 2π |
| 3 |
| 2π |
| 3 |
即
| ||
| 2 |
| 1 |
| 2 |
∴sin(B+
| π |
| 6 |
又0<B<
| 2π |
| 3 |
| π |
| 6 |
| π |
| 6 |
| 5π |
| 6 |
∴B+
| π |
| 6 |
| π |
| 2 |
∴B=
| π |
| 3 |
| π |
| 3 |
故△ABC是等边三角形.
| B |
| 2 |
| C |
| 2 |
| b2+c2−a2 |
| 2bc |
| 1 |
| 2 |
| 1 |
| 2 |
| π |
| 3 |
| B |
| 2 |
| C |
| 2 |
| π |
| 3 |
| 2π |
| 3 |
| 2π |
| 3 |
| 2π |
| 3 |
| 2π |
| 3 |
| ||
| 2 |
| 1 |
| 2 |
| π |
| 6 |
| 2π |
| 3 |
| π |
| 6 |
| π |
| 6 |
| 5π |
| 6 |
| π |
| 6 |
| π |
| 2 |
| π |
| 3 |
| π |
| 3 |