factor 10c^2-60cd +80d^2
\(10c^2-60cd +80d^2\)\((2c - 8d) (5c -10d)\)\(this \\ is \\ because...\)\(2c*5c=10c^2\)\(2c * -10d=-20cd \\ -8d*5c=-40cd \\ -20cd-40cd=-60cd\)\(-8d * -10d = 80d\)