Cho `tan \alpha = 1,5`. Tính `cos \alpha`, `sin \alpha`, `cot \alpha` ? Tính cách dễ hiểu nhất ạ

Ta có: `cot\alpha=1/{tan\alpha}`

`=>cot\alpha=1/{1,5}=1/{3/2}=2/3`

Lại có: `1/{sin^2\alpha}=1+cot^2\alpha`

`<=>1/{sin^2\alpha}=1+4/9=13/9`

`=>sin^2\alpha=9/13`

`=>sin\alpha=3/sqrt{13}`

`sin^2\alpha+cos^2\alpha=1`

`<=>9/13+cos^2\alpha=1`

`<=>cos^2\alpha=4/13`

`=>cos\alpha=2/sqrt{13}`