4+cosa+tg^2a если cosa=1\2

cosα =1/2 .---(4+cosα +tq²α) - ?4+cosα +tq²α =4+cosα +tq²α =4+cosα +(1-cos²α)/cos²α =4+1/2 +(1-(1/2)²)/(1/2)² =4+1/2 +(1-1/4)/(1/4) =4+1/2+(3/4)/(1/4)=4+1/2 +3 =7,5.