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hectictar

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 #2
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Find   (1+i2)46 .

 

Let's convert  1 + i  to polar form so we can use de Moivre's Theorem.

 

1+i=2(cosπ4+isinπ4)

 

Now lets raise both sides of that equation to the power of  46 .

 

(1+i)46=[2(cosπ4+isinπ4)]46 (1+i)46=(2)46(cosπ4+isinπ4)46

 

And divide both sides by  (2)46

 

(1+i)46(2)46=(cosπ4+isinπ4)46 (1+i2)46=(cosπ4+isinπ4)46

 

De Moivre's Theorem says....

 

(cos(x)+isin(x))n=cos(nx)+isin(nx)    So....

 

(cosπ4+isinπ4)46=cos(46π4)+isin(46π4) (1+i2)46=cos(46π4)+isin(46π4) (1+i2)46=cos(23π2)+isin(23π2)

 

Now let's find a reference angle that is coterminal with  23π2  by subtracting  2π  five times.

 

23π22π2π2π2π2π=23π210π=23π220π2=3π2

 

So....

 

(1+i2)46=cos(3π2)+isin(3π2) (1+i2)46=0+i(1) (1+i2)46=i

.
29.08.2018