Which one of the following quadratic equations will have one root

a) c^2 + 10c - 25 = 0
b) 5x^2+8x+16=0
c) y^2-9=0
d) 16y^2-8y+1=0
e) -9x^2 + 12x + 4=0

and why?

1.
-(-c+5 sqrt(2)-5) (c+5 sqrt(2)+5)=0
2.
(4+(1-2 i) x) (4+(1+2 i) x)=0
3.
(y-3)(y-3)=0
4.
(4y-1)^2
5.
(-3 x+2 sqrt(2)+2) (3 x+2 sqrt(2)-2)



Therefore only 3 and 4 have only one root.


Method 2:
Check the discriminant if it comes out to be negative, then the roots are complex conjugates of each other. If it comes out to be positive, then there are two distinct roots. If it turns out to be zero, then there is only one repeated root.
D=b^2-4ac