Find the necessary and sufficient condition that all the images of the function f (x) = (M2 + 4m-5) x2-4 (m-1) x + 3 are above the x-axis M < 1 or m > 4 1 ≤ m < 19, the intersection should be 4 ≤ m < 19, why not

Find the necessary and sufficient condition that all the images of the function f (x) = (M2 + 4m-5) x2-4 (m-1) x + 3 are above the x-axis M < 1 or m > 4 1 ≤ m < 19, the intersection should be 4 ≤ m < 19, why not

When m ^ 2 + 4m-5 is not equal to 0, M2 + 4m-5 > 0 opening upward M1 B ^ 2-4ac = 16 (m-1) ^ 2-12 (m ^ 2 + 4m-5) = 4m ^ 2-80m + 76