Answer:
(A) 10e^(i7π/4)
Explanation:
You want the exponential form of 5√2 -5i√2.
Complex number notation
There are numerous ways a complex number can be written in "polar form".
The usual choices are ...
a +bi . . . . . . . . . . . . . rectangular form
A(cos(θ) +i·sin(θ)) . . . . a sort of hybrid form
A·cis(θ) . . . . . . . . . . an abbreviation of the above
A∠θ . . . . . . . . . . . . polar form
A·e^(iθ) . . . . . . . . . using Euler's formula
Conversion
The conversion from rectangular form to any of the others makes use of trig identities and the Pythagorean theorem.
A = √(a² +b²)
θ = arctan(b/a) . . . . . with attention to quadrant
Application
For the given number, ...
A = √((5√2)² +(-5√2)²) = (5√2)√(1 +1) = 5·2
A = 10
θ = arctan(-5√2/(5√2)) = -1 . . . in the 4th quadrant
θ = 7π/4
Then the desired exponential form of the complex number is ...
10e^(i7π/4)
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Additional comment
Spreadsheets and some calculators have an ATAN2(x, y) function that performs a quadrant-sensitive angle conversion.