The line for the graph x=1 is the line of reflection that reflects triangle ABC onto triangle A'B'C'.
You have to find the middle points between each pair of identical points and then join them.
Answer:
Given that
sinθ = 0.8660
⇒ sinθ = 0.8660 = √3/2
⇒ θ = sin⁻¹(√3/2)
⇒ θ = 60°