(cos α-1) (1+cos α)=(cos α-1) (cos α+1)=cos^2 α-1=-sin^2a
3х-8 / 2 = -1
3х-8 = -2
3х = -2+8
3х = 6
х = 6:3
х = 2
2х - 5y = 10
y = 0
2x = 10
x = 5
Ответ ( 5 ; 0 )
7,5-x>0⇒x<7,5
lg(7,2)+lg(7,5-x)=1
7,2(7,5-x)=10
7,5-x=10/7,2=25/18
x=75/10-25/18=675/90-125/90=550/90=55/9=6 1/9
- +
------------------------|-------------------------------------->
1.5