If a = 2017, b = 2016, c = 2015, then
find a2 + b2 + c2 - ab - bc - ca.
Answer & explanation
Correct answer: option 4
a2 + b2 + c2 - ab - bc - ca = \(\frac{1}{2}\) [(a - b)2 + (b - c)2 + (c - a)2]
= \(\frac{1}{2}\) [(2017 - 2016)2 + (2016 - 2015)2 + (2015 - 2017)2]
= \(\frac{1}{2}\) [1 + 1 + 4] = 3