1 |
3 |
1 |
3 |
1 |
2 |
7 |
9 |
∴
a |
c |
| ||
3 |
(Ⅱ)cotB+cotC=
cosBsinC+cosCsinB |
sinBsinC |
sin(B+C) |
sinBsinC |
sinA |
sinBsinC |
由正弦定理和(Ⅰ)的结论得
sinA |
sinBsinC |
1 |
sinA |
a2 |
bc |
2 | ||
|
| ||
|
14 | ||
3
|
14
| ||
9 |
故cotB+cotC=
14
| ||
9 |
a |
c |
1 |
3 |
1 |
3 |
1 |
2 |
7 |
9 |
a |
c |
| ||
3 |
cosBsinC+cosCsinB |
sinBsinC |
sin(B+C) |
sinBsinC |
sinA |
sinBsinC |
sinA |
sinBsinC |
1 |
sinA |
a2 |
bc |
2 | ||
|
| ||
|
14 | ||
3
|
14
| ||
9 |
14
| ||
9 |