a)
`sin \hat{E}=(DF)/(EF)`
`cos \hat{E}=(ED)/(EF)`
`tan \hat{E}=(DF)/(DE)`
`cot \hat{E}=(DE)/(DF)`
b)
Áp dụng định lý Py-ta-go:
`DE^2+DF^2=EF^2`
`⇔EF=\sqrt{10^2+24^2}=26cm`
`sin \hat{E}=(DF)/(EF)=24/26=12/13`
`tan\hat{E}=cot \hat{F}=(DF)/(DE)=24/10=12/5`