Cos(5)Cos(55)Cos(65)=sin(5pi/36)sin(7pi/36)cos(5*)
1. 16-24*y+9*y^2-(3*y+4)^2+48*y
. 16-24*y+9*y^2-(9*y^2+24*y+16)+48*y
. 16-24*y+9*y^2-9*y^2-24*y-16+48*y
. 16-24*y-24*y-16+48*y
. 16-48*y-16+48*y
. -48*y+48*y
. 0
3 . 9*a^2-4-(3*a-4)^2-28=0
. 9*a^2-4-(9*a^2-24*a+16)-28=0
. 9*a^2-4-9*a^2+24*a-16-28=0
. -4+24*a-16-28=0
. -20+24*a-28=0
. -48+24*a=0
-24y²+1,4y-0,49=0
24y²-1,4y-0,49=0 1,4=7/5 0,49=49/100
D=(7/5)²+4*24*49/100)=49/25+24*49/25=25*49/25=49 √D=7
y1=(7/5+7)/(24*2)=(7+35)/(5*48)=42/(5*48)=7/(5*8)=7/40
y2=(7/5-7)/48=(7-35)/(5*48)=-28/(5*48)=-7/(5*12)=-7/60
ответ y1=7/40; y2= - 7/60