4x+7=2+8n
x=2n-1.25
2n>1.25 n>5/8 n=1 x=0.75
(3x-1)(3x+1)-(x-1)(x+2)=8
(9х²-1)-(х²+2х-х-2)=8
9х²-1-х²-х+2=8
8х²-х+1-8=0
8х²-х-7=0
Д= 1-4*8*(-7)=225
х₁= 1-15/16=-14/16= -7/8
х₂=1+15/16=1
у¹= 12х¹¹+cosx
y¹=2x sinx+x²cosx=x(2sinx+x cosx)