If a + b + c = 26 and ab + bc + ca = 109, find the value of a² + b² + c² = ?

Solution (By Examveda Team)

$$\eqalign{ & {\left( {a + b + c} \right)^2} = {\text{ }}{a^2} + {b^2} + {c^2} + 2\left( {ab + bc + ca} \right) \cr & \Rightarrow {\left( {26} \right)^2} = {\text{ }}{a^2} + {b^2} + {c^2} + 2\left( {109} \right) \cr & \Rightarrow {a^2} + {b^2} + {c^2} = 676 - 218 \cr & \Rightarrow {a^2} + {b^2} + {c^2} = 458 \cr} $$