Answer:
We have the equation:
(ax^2 + 3x + 2b) - (5x^2+bx-3c)= 3x^2 - 9
First, move all to the left side.
(ax^2 + 3x + 2b) - (5x^2+bx-3c) - 3x^2 + 9 = 0
Now let's group togheter terms with the same power of x.
(a - 5 - 3)*x^2 + (3 - b)*x + (2b + 3c + 9) = 0.
This must be zero for all the values of x, then the things inside each parenthesis must be zero.
1)
a - 5 - 3 = 0
a = 3 + 5 = 8.
2)
3 - b = 0
b = 3.
3)
2b + 3c + 9 = 0
2*3 + 3c + 9 = 0
3c = -6 - 9 = -15
c = -15/3 = -5
Then we have:
a = 8, b = 3, c = -5
a + b + c = 8 + 3 - 5 = 6