sin 6x cos x + cos 6x sin x =sin(6x+x)=sin7x
sin 7x = 1/2
7x = (-1)^n (pi/6)+pin
x = (-1)^n (pi/42) + pin/7
2X^2 - 3X - 2 = 0
D = 9 + 16 = 25 ; V D = 5
X1 = ( 3 + 5 ) : 4 = 2
X2 = ( - 2 ) : 4 = ( - 0,5 )
Ответ 2 и ( - 0,5 )
Решение.....................
A4=a1+3d
a12=a1+11d
a1+3d=17 (1)
a1+11d=7 (2)
(1)-(2): 3d-11d=17-7
-8d=10
d=-10/8
d=-5/4
a1=17-3d=17-3*(-5/4)=17+15/4=83/4=20.75
A-b²
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