Question

解方程x²+ax+1=0

Answer 1

△=a²-4≥0是有实数根
即a≤-2或a≥2时方程有实数根
x1=[-a+√（a²-4）]/2
x2=[-a-√（a²-4）]/2

Answer 2

x1 = (-a + (a^2-4))/2
x2 = (-a - (a^2-4))/2

Answer 3

x1 = (-a + (a^2-4))÷2
x2 = (-a - (a^2-4))÷2