原式＝(cos24)^2+1-(cos6)^2+(cos18)^2 ＝(1＋cos48-1-cos12+1+cos36）/2+1 ＝(cos48-cos12+1+cos36)/2+1 ＝[cos(60-12)-cos12+cos36+1〕/2+1 ＝[1/2cos12+根号3/2sin12-cos12+cos36+1〕/2+1 ＝[根号3/2sin12-1/2cos...