sinB |
sinA |
∴C为钝角,sinB=-2sinAcosC.
又sinB=sin(A+C)=sinAcosC+cosAsinC,
∴sinAcosC+cosAsinC=-2sinAcosC,即cosAsinC=-3sinAcosC,
∴tanC=-3tanA,
∴tanB=-tan(A+C)=-
tanA+tanC |
1−tanAtanC |
−2tanA |
1+3tan2A |
2 | ||
|
2 | ||
2
|
| ||
3 |
当且仅当
1 |
tanA |
| ||
3 |
则tanB的最大值为
| ||
3 |
故选:A.
sinB |
sinA |
| ||
3 |
| ||
2 |
sinB |
sinA |
tanA+tanC |
1−tanAtanC |
−2tanA |
1+3tan2A |
2 | ||
|
2 | ||
2
|
| ||
3 |
1 |
tanA |
| ||
3 |
| ||
3 |