`text{Xét ΔABC có}`
`+) cos A = (b^2 + c^2 - a^2)/(2bc) = (13^2 + 15^2 - 24^2)/(2.13.15) = -7/15`
`-> hat{A} ≈ 117^0 \49'`
`+) cos B = (c^2 + a^2 - b^2)/(2ac) = (15^2 + 24^2 - 13^2)/(2.15.24) = (79)/(90)`
`-> hat{B} ≈ 28^0 \37'`
`-> hat{C} = 180^0 - hat{A} - hat{B} = 33^0 \34'`