sinBsinC |
cosBcosC |
所以
cosA |
cos(B−C) |
−cos(B+C) |
cos(B−C) |
=
sinBsinC−cosBcosC |
cosBcosC+sinBsinC |
=
5cosBcosC−cosBcosC |
cosBcosC+5cosBcosC |
=
2 |
3 |
故答案为:
2 |
3 |
cosA |
cos(B−C) |
sinBsinC |
cosBcosC |
cosA |
cos(B−C) |
−cos(B+C) |
cos(B−C) |
sinBsinC−cosBcosC |
cosBcosC+sinBsinC |
5cosBcosC−cosBcosC |
cosBcosC+5cosBcosC |
2 |
3 |
2 |
3 |