Question 1197660
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Hi
Checking Your Work 
5. √(-243) =  √(-1)(243) = 15.5885i

6.{{{ 2*sqrt(-81) - 2sqrt(-100) }}} = 18i - 20i = -2i

7. NOte:  i = {{{sqrt(-1)}}}  ⇒ i^2 = -1

{{{(2i - 5)/(i + 1) = ((2i - 5)(i - 1)) / ((i + 1)(i - 1))}}}
       = {{{ (2i^2 - 7i + 5)/(-2) = -((-2 - 7i + 5)/2) = (-3 + 7i)/2}}}  

Wish You the Best in your Studies.
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