Which equation has exactly one real solution?

Question

A 4x^2– 12x– 9 = 0
B 4x^2+ 12x+ 9 = 0
C 4x^2– 6x– 9 = 0
D 4x2+ 6x+ 9 = 0
Please teach me how to do this

Answer 1

Have you learned about b^2 - 4ac, called the discriminant, of the quadratic equation?

If the discriminant is zero, there is only one solution, so evaluate b^2 - 4ac.
If the discriminant is positive, there are 2 real and different solutions,
If the discriminant is negative, there are no real solutions

I will do A, you do the others to decide.

A:
4x^2 - 12x - 9 = 0 , a=4, b=-12, c = -9
b^2 -4ac
= 144-4(4)(-9) = + , so there are two different real solutions.

B: