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Questions  

Principal argument of z=i1i1cos2π7+sin2π7 is 

a
π28
b
3π28
c
17π28
d
19π28

detailed solution

Correct option is C

i1−cos⁡2π7+sin⁡2π7=2isin2⁡π7+2sin⁡π7cos⁡π7=2sin⁡π7cos⁡π7+isin⁡π7Also , i−1=2−12+i2=2cos⁡3π4+isin⁡3π4∴ z=22sin⁡π7cos⁡3π4−π7+isin⁡3π4−π7 =22sin⁡π7cos⁡17π28+isin⁡17π28Thus , arg⁡(z)=17π28.

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