Subtract $\sqrt { - 81 } - \sqrt { - 4 }$ and write in standard form.
A) $22 i$
B) $11 i$
C) $\sqrt { - 7 } i$
D) $7 i$
E) $- 7 i$

Name: Subtract $\sqrt { - 81 } - \sqrt { - 4 }$ and write in standard form. A) $22 i$ B) $11 i$ C) $\sqrt { - 7 } i$ D) $7 i$ E) $- 7 i$
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Question

Quizplus · Accepted Answer

$$\sqrt{-81}-\sqrt{-4}=\sqrt{81}\cdot\sqrt{-1}-2\cdot\sqrt{-1}=9i-2i=7i$$

The answer is a purely imaginary number, and the only choice that is purely imaginary is D, 7i.

Subtract −81−−4\sqrt { - 81 } - \sqrt { - 4 }−81​−−4​

Subtract $\sqrt { - 81 } - \sqrt { - 4 }$