Đáp án:
`sin42^o-cos48^o`
`=sin42^o-sin42o`(do `42^{o}+48^o=90^o`)
`=0`
`sin^2 61^{o}+sin^{2}29^{o}`
`=sin^{2}61^{o}+cos^{2}61^o`
`=1`
`cos^{2}38^{o}+cos^{2}52^{o}+cos^{2}60^o`
`=cos^{2}38^{o}+sin^{2}38^{o}+cos^{2}60^o`
`=1+cos^{2}60^o`
`=1+1/4=5/4`.