For a complex number z, find the minimum value of ∣z−3∣2+∣z−5+2i∣2+∣z−1+i∣2.
Solution — click to reveal
Let z=x+yi, where x and y are real numbers. Then ∣z−3∣2+∣z−5+2i∣2+∣z−1+i∣2=∣x+yi−3∣2+∣x+yi−5+2i∣2+∣x+yi−1+i∣2=∣(x−3)+yi∣2+∣(x−5)+(y+2)i∣2+∣(x−1)+(y+1)i∣2=(x−3)2+y2+(x−5)2+(y+2)2+(x−1)2+(y+1)2=3x2−18x+3y2+6y+40=3(x−3)2+3(y+1)2+10≥10.Equality occurs when x=3 and y=−1, so the minimum value is 10.