Using the collocation method, it is proved that the value of the algebraic formula - 10x2 + 7x-4 is always less than 0. From the above conclusion, can you write three quadratic trinomial formulas whose values are always greater than 0, and the coefficients of the quadratic terms are l, 2, 3?

Using the collocation method, it is proved that the value of the algebraic formula - 10x2 + 7x-4 is always less than 0. From the above conclusion, can you write three quadratic trinomial formulas whose values are always greater than 0, and the coefficients of the quadratic terms are l, 2, 3?

It is proved that: ∵ - 10x2 + 7x-4 = - 10 (x-720) 2-11140, and - (x-720) 2 ≤ 0, - 11140 < 0, ∵ - 10 (x-720) 2-11140 < 0, that is: - 10x2 + 7x-4 < 0, ∵ the value of algebraic formula - 10x2 + 7x-4 is always less than 0. Examples: ① x2 + 2x + 2, ② 2x2-4x + 8, ③ 3x2 + 6x + 8