I'm guessing you have set this equal to zero. If so:
let a = 4; b = -1; and c = 7. See where these numbers came from? Evaluate b^2 - 4ac
You get -111. This means your answer is an imaginary number because the solution =
[(-b)+-SQR(b^2 - 4ac) ]/ 2a
So you get: [1 +- SQR(111) i] / 8
Note: SQR(-111) = SQR(-1) * SQR(111) = SQR(111) i because SQR(-1) = i , the imaginary number.
Its imaginary because no number multiplied by itself = -1, however i^2 = -1 and i^4 = 1. Do you see why?