Why does l1+ il = v(1+1)

Question

Please explain why l1+il = √(1+1) is true? It is a step in working out the question: prove that l(3+i)/(2-i)l = √2.

Answer 1

1+i = 1+1i has real part a = 1 and imaginary part b = 1, so it has absolute value |1+i| = √(a²+b²) = √(1²+1²).