Question

$ifab + bc + ca = 36 \: \\ a {}^{2} + b { }^{2} + c {}^{2} = 85 \\ find \: a + b + c = {?}^{}$
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Answer 1

(a+b+c)² = a²+b²+c²+2(ab+bc+ca)

(a+b+c)²= 85+2(36)

= 85+72= 157

a+b+c = √157