If $z=x+iy$, what is the modulus $|z|$? 
A$x+y$
B$\sqrt{x^2+y^2}$
C$x^2+y^2$
D$\sqrt{x^2-y^2}$
Answer & Solution
Correct answer: B. $\sqrt{x^2+y^2}$
For $z=x+iy$, the modulus is the distance of the point $(x,y)$ from the origin in the Argand plane. Hence $|z|=\sqrt{x^2+y^2}$.
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