如图，∵在Rt△ACB中，∠C=90°，tanA=| BC |
| AC |
| BC |
| AB |
| AC |
| AB |
∴
| sinA |
| cosA |
| ||
|
| BC |
| AC |
∴tanA=
| sinA |
| coaA |
∵tanA=2，
∴
| sinA |
| cosA |
∴
| 3sinA+cosA |
| 4cosA−5sinA |
=
| ||
4−
|
=
| 3tanA+1 |
| 4−5tanA |
=
| 3×2+1 |
| 4−5×2 |
=-
| 7 |
| 6 |
| 3sinA+cosA |
| 4cosA−5sinA |
如图，∵在Rt△ACB中，∠C=90°，tanA=| BC |
| AC |
| BC |
| AB |
| AC |
| AB |
| sinA |
| cosA |
| ||
|
| BC |
| AC |
| sinA |
| coaA |
| sinA |
| cosA |
| 3sinA+cosA |
| 4cosA−5sinA |
| ||
4−
|
| 3tanA+1 |
| 4−5tanA |
| 3×2+1 |
| 4−5×2 |
| 7 |
| 6 |