If the line y = 2x + 1 is a tangent of the curve y = x ^ 3-x-a, find the value of the real number a

If the line y = 2x + 1 is a tangent of the curve y = x ^ 3-x-a, find the value of the real number a

y'=3x^2-1=2
X = ± 1, y = 3 or - 1
Substitute y = x ^ 3-x-a to get
a=-3,a=1