maths

a^2 + a - 12345765432 = 0
a = 111111 or - 111112

b^2 -3b - 12345987654 = 0
b = 111114 or -111111

we know if ax^2 + bx +c = 0 = [x-(z1)][x-(z2)]
z1*z2 = c/a

12345765432=33411 x 369512
Therefore, sqrt(12345765432) = sqrt(33411) x sqrt(369512) = 182.78 x 607.87.
By quadratic equation formula,
a= {-1 +/- sqrt[1 + 4 x 12345765432]}/2 = {-1 +/- (2 x sqrt(12345765432)}/2
= -0.5 +/- sqrt(12345765432) = -0.5 +/- 182.78 x 607.87 = -0.5 +/- (111111.46).
Therefore a = 111111 or -111112.
Same method can be used to solve the second question.

最快捷計算我未必知。
個人建議應是將數字做短除，搵因子。
之後再按題目解。