Question

if a + b + C is equal to 15 and a square + b square + c square is equqal to 3 find the value of AB + BC + AC
$7\sqrt{x} \div 8 \sqrt{x}$
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Answer 1

${a}^{2} + {b}^{2} + {c}^{2} = a + b + c \times 2{ab + bc + ca} \\ \\ 3 = 15 \times 2 \: ({ab + bc + ca}) \\ \frac{3}{15} = 2(ab - bc - ca) \\ \frac{1}{10} = (ab+ bc + ca)$