Evaluate : $8 (x + y)^{2} - 26 (x + y) + 15$ = $0$

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Solution

# $8 (x + y)^{2} - 2 b (x + y) + 15 = 0$ Let $x + y = t$
$8 t^{2} - 26 t + 15 = 0$
$t = \frac{26 \pm \sqrt{676 - 480}}{2 \times 8} = \frac{26 \pm \sqrt{196}}{16} = \frac{3}{4}, \frac{5}{2}$ .
$\Rightarrow x + y = 3 / 4$ & $x + = 5 / 2$ .

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