How many of the following represent a line in R 3 ?

• x = (2, 1, 3) + s(1, −1, 2)
• x = (1, 2, −1) + s(1, 1, −2) + t(2, 2, −4)
• x = (1, −1, 2) + s(1, 1, 2) + t(3, −1, 4)
• 2x + 3y + z = 2