Formula method: Convert the quadratic equation of one variable into a general form, and then calculate the value of the discriminant △=b2-4ac. When B2-4ac is greater than or equal to 0, substitute the values of the coefficients a, b and c into the root-finding formula X = [-B (B 2-4ac) (1/2)]/(2A).

When using the formula method, it is not necessary to use a complete formula. Among them, b 2-4ac is also called the discriminant of quadratic equation in one variable, which is often expressed as. The coincidence of discriminant determines the root of quadratic equation in one variable:

When < 0, the unary quadratic equation has no real root. At this time, in the range of real numbers, it is not necessary to continue to use the complete formula to find the root, just explain that "the equation has no real root".

When =0, the quadratic equation of one variable has two equal real roots, because the square root of 0 is still 0, so the root of the equation is x=-b/(2a), which is exactly the form of the symmetry axis corresponding to the parabola Y = AX 2+BX+C.

Only when > 0, the quadratic equation of one variable has two unequal real roots, so the whole formula for finding the roots is needed. At this time, just substitute the three parameters of the equation. However, it must be noted that it is completely wrong to directly express the root of the unary quadratic equation BX 2+AX+C = 0 or AX 2-BX+C = 0, which involves the source of the formula for finding the root.