Question

ab+bc+ca=27 and a2+b2+c2=90find a+b+c​

Answer 1

$ab + bc + ca = 27 \\ {a}^{2} + {b}^{2} + {c}^{2} = 90 \\ we \: need \: to \: find \: a + b + c \\ ( {a + b + c})^{2} = {a}^{2} + {b}^{2} + {c}^{2} + 2(ab + bc + ca) \\ ( {a + b + c})^{2} = 90 + 2 \times 27 \\ ( {a + b + c})^{2} = 144 \\ a + b + c = 12$