If a + b + c = 9 and ab + bc + ca = 26 find the value of a^2 + b^2 + c^2.
a + b + c = 9 square both sides and simplify to
a^2 + b^2 + c^2 + 2 (ab + bc + ac) = 81
a^2 + b^2 + c^2 + 2 ( 26) = 81
a^2 + b^2 + c^2 = 29
+37167 
