2x^2 + 4x - 1 = 6 rearrange as
2x^2 + 4x - 7 = 0
Call the solutions a, b
The sum of these solutions = -4/2 = -2 = a + b
The product of these solutions = -7/2 = ab ⇒ 2ab = -7 (1)
So
a + b = -2
Square both sides
a^2 + 2ab + b^2 = 4 (2)
Sub (1) into (2)
a^2 - 7 + b^2 = 4 add 7 to both sides
a^2 + b^2 = 11