Tính giá trị biểu thức sau:
a) \(4\frac{1}{7}\)+\(\frac{-1}{6}\). ( 12 - \(5\frac{1}{7}\))
b) ( 2 + 4 + 6 + 8 +...+2014) - ( 3 + 5 + 7 + 9 +...+ 2011 )
c) ( 1 -\(\frac{1}{3}\)) . ( 1 - \(\frac{1}{6}\)) . ( 1 - \(\frac{1}{10}\)) . ( 1 -\(\frac{1}{15}\)) . ... . ( 1 -\(\frac{1}{780}\))