740
sina*(-cosa)*(-tga)/[-sina*(-cosa)*(-ctga)=-ctga*tga/ctga=-tga
7.41
(sin²a-cos²a)(sin²a+cos²a)-sin²a+cos²a=sin²a-cos²a-sin²a+cos²a=0
7.42
tg²a/(1+tg²a)*(1+1/tg²a)/(1/tg²a)=tg²a/(1+tg²a) *tg²a*(tg²a+1)/tg²a=tg²a
7.43
(2sinasin2a+2sinasin6a)/(2sin2acosa+2sin6acosa) *2ctga=
=2sina(sin2a+sin6a)/[2cosa(sin2a+sin6a)] * 2ctga=tga*2ctga=2
7.44
(2cos²²a+2cos2acosa)/[5cosa(cosa+cos2a)]=
=2cosa(cosa+cos2a)/[5cosa(cosa+cos2a)]=2/5=0,4