Tangent lines to the curve
I need to find out the tangent lines to the curve f (X) = 2X² - 8X + 3,
Which are parallels to line X + 2Y + 1 = 0.
I have slope of line : m = -1/2,
and derivative : f'X = 4X - 8,
I made : m = f'X,
and I obteined : X = 1 7/8,
I replace in : f(X) and reach to Y = -4 31/32,
With those values I get Y intersection = -129/32.
Then I built my equation,
but I think something is wrong, cause those are a very big fractions.
But I cant find the mistake. Maybe someone could show me the error in this operation?