Ответы и объяснения

2013-01-27T17:57:46+04:00

cosDEF = (DE^2 + EF^2 - DF^2) / (2*DE*EF) = (25+16-64) / (2*5*4) = -23 / 40
cosDFE = (DF^2 + EF^2 - DE^2) / (2*DF*EF) = (64+16-25) / (2*4*8) = 55 / 64
cosEDF = (ED^2 + DF^2 - EF^2) / (2*ED*DF) = (64+25-16) / (2*8*5) = 73 / 80