Wait is there any specific number that we have to use ?
None of them really, but C is equivalent to the Triognometric Pythagorean Theorem:



That's the Trigonometric Pythagorean Theorem
Answer: C
A complex number is made of two parts: one real part (without i) and one imaginary part (with i).
The conjugate of a complex number is found by inverting the sign of the imaginary part of the number.
Therefore, the conjugate of 10+3i is 10−3i