# Chapter 8 - Section 8.1 - Solving Quadratic Equations by Completing the Square - Exercise Set - Page 484: 112

$3\text{ pieces}$

#### Work Step by Step

Substituting $p=7$ in the given equation, $p=-x^2+15 ,$ results to \begin{array}{l}\require{cancel} 7=-x^2+15 \\ x^2=15-7 \\ x^2=8 .\end{array} Taking the positive square root of both sides (since $x$ is nonnegative), the equation above is equivalent to \begin{array}{l}\require{cancel} x=\sqrt{8} \\ x\approx3 .\end{array} Hence, the demand for the desk lamp, $x,$ is $3\text{ pieces} .$

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