Question

If a+b+c =9 and ab+bc+ca=23, then a+b+c squre=

Answer 1

given
a + b + c = 9
a b + bc + ca = 23
by using formula
(a + b + c)^2=a^2+ b^2+ c^2+ 2ab + 2bc + 2ca
(9)^2 =a^2 + b^2 + c^2 +2(23)
81. =a^2 + b^2 + c^2
$a {}^{2} + b ^{2} + c {}^{2} = 81 - 46 \\ a {}^{2} + b {}^{2} + c ^{2} = 35$