18x-30-50x+20=6x-2
18x-50x-6x=-2+30-20
-38x=8
x=-8/38
5/9x - 2/3x=20-11,
-1/9x=9,
x= 9:(-1/9),
x=-81.
(bn)- геом. прогр.
b1=27
b3=3
q-?
bn²=bn-1*bn+1
b2=√27*3=9
q=bn+1:bn
q=1:3
Cosa=8/17
sina=-√(1-cos²a)=-√(1-64/289)=-√(225/289)=-15/17
sin2a=2sinacosa=2*(-15/17)*8/17=-240/289