If the function ax^2+bx+c has a minimum value -5 when x=-1 and 0 when x=-2 , find the values of a , b and c .

This is what i did :

Let .. completing the square

when

... b=2a -- 1

... 4ac-b^2=-20a -- 2

Combining gives me --3

x=-2 when y=0

--- 4a=b ... 4

... 5

combining , --- 6

Now , combining 3 and 6 , .. or

i just couldnt find my mistake . thanks .