| 5 |
| 13 |
∴B为钝角，A，C为锐角，
∴sinB=
| 1−cos2B |
| 12 |
| 13 |
∵cosC=
| 4 |
| 5 |
∴sinC=
| 1−cos2C |
| 3 |
| 5 |
∴sinA=sin（B+C）=sinBcosC+cosBsinC=
| 33 |
| 65 |
∵AB=13，由正弦定理得
| BC |
| sinA |
| AB |
| sinC |
∴BC=
| ABsinA |
| sinC |
| 33 |
| 65 |
| 5 |
| 3 |
| 5 |
| 13 |
| 4 |
| 5 |
| 5 |
| 13 |
| 1−cos2B |
| 12 |
| 13 |
| 4 |
| 5 |
| 1−cos2C |
| 3 |
| 5 |
| 33 |
| 65 |
| BC |
| sinA |
| AB |
| sinC |
| ABsinA |
| sinC |
| 33 |
| 65 |
| 5 |
| 3 |