3x^2+bx+1=0 if the quardratic equation has no real roots,so i would like to ask the values of b

To see if the quadratic equation has no real roots, look at the discriminant, that is b² - 4ac, or in this case: b² - 12.  

 If this is negative then the equation has no real roots.

So, if -√(12) < b < √(12) then the equation has no real roots.

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