Question #23b88

1 Answer
Feb 11, 2018

# \ #

# "The answer is:" \qquad \qquad \qquad 125i. #

Explanation:

# \ #

# "This can be done quickly by de Moivre's Theorem --" #
# \qquad \qquad \qquad "and the result comes out beautifully." #

# "Here we go:" #

# "First, let's recall de Moivre's Theorem:" #

# \qquad \qquad \qquad ( cos( \theta ) \ + \ isin( \theta ) )^n \ = \ cos( n \theta ) \ + \ isin( n \theta ). #

# "Thus:" #

# \qquad \qquad [ 5 ( cos(30^0) \ + \ isin(30^0) ) ]^3 \ = #

# "Rules of Exponents:" #

# \qquad \qquad \qquad \qquad \qquad \quad = \ 5^3 ( cos(30^0) \ + \ isin(30^0) )^3 #

# "Applying de Moivre's Theorem:" #

# \qquad \qquad \qquad \qquad \qquad \quad = \ 5^3 ( cos( 3 \cdot 30^0 ) \ + \ isin( 3 \cdot 30^0) ) #

# \qquad \qquad \qquad \qquad \qquad \quad = \ 5^3 ( cos( 90^0 ) \ + \ isin( 90^0) ) #

# \qquad \qquad \qquad \qquad \qquad \quad = \ 5^3 ( 0 \ + \ ( i \cdot 1) ) #

# \qquad \qquad \qquad \qquad \qquad \quad = \ 5^3 ( i ) #

# \qquad \qquad \qquad \qquad \qquad \quad = \ 125 ( i ) #

# \qquad \qquad \qquad \qquad \qquad \quad = \ 125i. #

# \ #

# "Thus:" #

# \qquad \qquad \qquad \qquad \quad [ 5 ( cos(30^0) \ + \ isin(30^0) ) ]^3 \ = \ 125i. #