Math
posted by Matt .
Which of the following are linear equations in x1, x2 and x3?
(a) x1 + 5x2 − (2^0.5)x3 =1
(b) x1 + 3x2 + x1.x3 = 2
(c) x1 = −7x2 + 3x3
(d) x1^−2 + x2 + 8x3 =5
(e) x1^3/5 − 2x2 + x3 = 4
(f) πx1 − (2^0.5)x2 + 13x3 = 7^1/3

a, c, f