Vẽ \(\Delta\)ABC, biết:

a, A(1,1); B(2,5); C(4,-1)

b, A(-180,-30); B(-60,60); C(90,15)

\(\frac{2}{1.3}+\frac{2}{3.5}+...+\frac{2}{2015.2017}\)

= \(\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+...+\frac{1}{2015}-\frac{1}{2017}\)

= \(\frac{1}{1}-\frac{1}{2017}\)

= \(\frac{2016}{2017}\)