78 пассажиров - 60% (100%-40%)
х пассажиров - 100%
78*100=60*х
60х=7800
х=130
1) x+8<0
x<-8
2) cos2a + cos14a + cos6a + cos10a =
(cos14a + cos2a) + (cos10a + cos6a) =
(2 * cos((14a + 2a) / 2) * cos((14a - 2a) / 2)) +
(2 * cos((10a + 6a) / 2) * cos((10a - 6a) / 2)) =
2 * cos(8a) * cos(6a) +
2 * cos(8a) * cos(2a) = 2cos(8a) * (cos6a + cos2a) =
2cos(8a) * (2cos((6a+2a)/2)*cos((6a-2a)/2)) =
<span>4cos(8a) * cos(4a) * cos(2a)
3) a2=a1+d
d=3-1=2
Sn = (a1+an) *n/2 = (1+x)*n/2 =625
1+x= 1250/n
n=1250/(1+x) = 1250 + 1250/x
2a1+d*(n-1)=1+x=1250/n
2+2*(n-1) = 1250/n
2+2n-2 =1250/n
2n=1250/n
3n=1250
n=416,6</span>
1) - 3х^2+4х-7=0 - корней нет
![2) \: 2 {x}^{2} - 7x + 8 = 0 \\ \\ d = ( - 7)^{2} - 4 \times 2 \times 8 = 49 - 64 = - 15](https://tex.z-dn.net/?f=2%29+%5C%3A+2+%7Bx%7D%5E%7B2%7D++-+7x+%2B+8+%3D+0+%5C%5C++%5C%5C+d+%3D+%28+-+7%29%5E%7B2%7D++-+4+%5Ctimes+2+%5Ctimes+8+%3D+49+-+64+%3D++-+15+)
корней нет
(х-2,5)²=49
х²-2,5²=49
х²-2,5²=7²
х²=7²+2,5²
х=√49+6,25
х1=-√55,25
х2=√55,25
можно и так:
(х-2,5)²=49
х²-6,25=49
х²=49+6,25
х²=55,25
х1=-√55,25
х2=√55,25