1. 6sin^2x-5+5cosx=0
6(1-cos^2x)+5cosx-5=0
6-6cos^2x+5cosx-5=0
-6cos^2x+5cosx+1=0
cosx=t
-6t^2+5t+1=0
D=b^2-4ac D=25-4*(-6)*1=49sx
t12=(-5+-7)/(-12) t1=1 t2=-1/6
cosx=1 x=2πn, n∈Z
cosx=-1/6 x= +-(π-arccos1/6)+2πn, n∈Z
sin2x+sin6x=2sin4xcos2x
sin4x=2sin2xcos2x=4sinxcosx(cos^2x-sin^2x)
cos50+sin80=cos(90-40)+sin80=sin40+sin80=2sin60cos20=√3cos20
D = 16 + 84 = 100 ; √ D = 10
X1 = ( 4 + 10) : 2 = 7
X2 = ( 4 - 10 ) : 2 = - 3
Один ответ у каждого уравнения
1) x-7=0
х=7
2)17+x=20
х=20-17
х=3
3)2x-5=3
2х=3+5
2х=8
х=4
4)5-2x=3
-2х=3-5
-2х=-2
х=1