# Chapter 11 - Quadratic Functions and Equations - 11.1 Quadratic Equations - 11.1 Exercise Set: 18

$t=\pm 2i$

#### Work Step by Step

Since $x^2=a$ implies $x=\pm\sqrt{a}$ (the Square Root Principle), the solutions to the given equation, $t^2+4=0 ,$ are \begin{array}{l}\require{cancel} t^2=-4 \\\\ t=\pm\sqrt{-4} \\\\ t=\pm\sqrt{-1}\cdot\sqrt{4} \\\\ t=\pm i\cdot2 \\\\ t=\pm 2i .\end{array}

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