If a2 + b2 + c2 = 6.25 ab + bc + ca = 0.52 find a + b + c if a + b + c < 0

±2.7 -2.7 ±2.8 -2.8

-2.7

(a + b + c)2 = a2 + b2 + c2 + 2(ab + bc +ca) (a + b + c)2 = 6.25 + 2×0.52 a + b + c =\(\sqrt {7.29}\) = 2.7 a + b + c = -2.7 (a + b + c < 0)