2sin²(x) + sin(x)cos(x) = 1, tg(2x) = ?
1 = sin²(x) + cos²(x)
sin(x)cos(x) = sin(2x)/2
cos²(x) - sin²(x) = cos(2x)
sin(2x)/2 = cos²(x) - sin²(x)
sin(2x)/2 = cos(2x)
sin(2x)/cos(2x) = 2 = tg(2x)
