The Total solution for NCERT class 6-12
a2 +b2 + c2 = 20, a + b + c = 0∴ (a + b+ c)2 = 0a2 + b2 + c2 + 2(ab + bc + ca)= 0⇒ 20 + 2(ab + be + ca) = 0⇒ 2(ab + bc + ca) = -20ab + bc + ca = −202 =-10