Let z1=2-i,z2=-2+i

Question

Find. Re(z1z2/modulus of z1)

I only know that modulus of z1=
2+i

I have no idea . how to solve this?

Answer 1

the modulus of z1 = |2-i| = √(2^2+1^2) = √5

z1•z2 = (2-i)(-2+i) = -3+4i

so, Re(z1•z2)/√5 = -3/√5

Answer 2

But the answer should be -2/5

Answer 3

In that case, look for a typo somewhere. The numbers you gave produce the given result.