Question

If d + e + f = 11 , de + ef + fd = 60, find the value of d2 + e2 + f2

Answer 1

${(d + e + f)}^{2} = {d}^{2} + {e}^{2} + {f}^{2} + 2 \times (de + ef + fd)$
$thus \\ {d}^{2} + {e}^{2} + {f}^{2} = {11}^{2} - 2 \times 60 \\ = 121 - 120 = 1$