6/19
Объяснение:
tgx = 3
↓
x = arctg(3)
sin²(arctg(a)) = a²/(1+a²)
↓
sin²(x) = sin²(arctg(3)) = 9/(1+9) = 9/10 = 0,9
cos²(arctg(a)) = 1/(1+a²)
↓
cos²(x) = cos²(arctg(3)) = 1/(1+9) = 1/10 = 0,1
↓
y = (sin²x-3cos²x)/(2sin²x+cos²x) = (0,9-0,3)/(1,8+0,1) = 0,6/1,9 = 6/19
