Modulus Argument form!

Level pending

Let z1= r(cosπ/4 + isinπ/4) and z2= 1+√3i. Write z2 in modulus argument form.

Bonus question (not part of the answer): For those who are smarter or more BRILLIANT, find the value of r if modulus(z1 X z2^3) =2. Post the answer for this bonus question as part of your comment below!

Assumptions: For z1, the term "i" in "isinπ/4" refers to the imaginary number i. For z2, the term "i" is outside the squareroot but is multiplied to √3, so √3i = i√3.

Note: Since Brilliant only allows answers to be in numbers for math problems, let option 1 be 2[cos π/3+isin π/3], option 2 be 4[cos π/4+isin π/4], option 3 be 2[cos π/4+isin π/4], option 4 be 4[cos π/6+isin π/6].

3 1 2 4

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

2 solutions

Jeremy Soh
Jan 14, 2014

Let z2= 1+sqrt3 i.

Angle Theta = tan-1 (sqrt3) = pi/3 rad.

Therefore, arg z = pi/3 rad.

r = modulus(z) = sqrt (1^2+(sqrt3)^2) = 2.

Therefore, z2 = 2(cos pi/3 + isin pi/3).

Therefore, option 1 is the answer.

P.s. Lazy to do the bonus question and I am not smart enough. Others please advise on how to do the bonus question!

Correct!

Nicholas Wei - 7 years, 4 months ago
Ankush Gogoi
Aug 22, 2014

r=1/4..z2= 2(cos pi/3 + isin pi/3) so using de moivre's theorem we get z2 ^3 = 8(cos pi + isin pie) = -8...so z1 z2 ^3 = r(cos pi/4 + isin pi/4) (-8)....taking modulus we get mod(z1 z2 ^3)= r 1*8(since mod(cos pi/4 +isin pi/4)=1) implies 2=8r so r=1/4...

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...