Simplify the number using the imaginary unit i:

(square root) -28

options:
a. 2(square root) -7
b. -2(square root) -7
c. i(square root) 28
d. 2i(square root) 28

We have to simplify:
√ ( - 28 )
We know that √ (-1 ) = i ( the imaginary unit )
√ ( - 28 ) = √ 28 * ( - 1 ) = i √ ( 28 ) = i √ ( 4 * 7 ) = 2 i √( 7 )
But there is not such solution among the options.
Only correct answer ( using the imaginary unit ) is:
C. i (square root) 28