xxpensartxx xxpensartxx 03-07-2019 Mathematics contestada Choose the expression that represents a quadratic expression. a. 9x - 2 b. 5x^2 + 9x - 1 c. -2x^3 + 8x^2 - 7x + 1 d. x^4 - 12x^3 + 8x^2 - 7x + 1