Answer:
C = 25/9
Step-by-step explanation:
Consider the perfect square trinomial ...
(x -a)² = x² -2ax +a²
The constant (a²) is the square of half the x-coefficient.
For your trinomial, the square of half the x-coefficient is ...
C = ((-10/3)(1/2))² = (5/3)² = 25/9
