1-2sin²3x = 1 - 2(1-cos²3x)1-2sin²3x = 1 - 2 + 2cos²3x1-2sin²3x = -1 + 2cos²3x1-2sin²3x = 2cos²3x - 1
1-2sin²3x = 1 - 2(1-cos²3x)
1-2sin²3x = 1 - 2 + 2cos²3x
1-2sin²3x = -1 + 2cos²3x
1-2sin²3x = 2cos²3x - 1