I’m so confused on this. Someone please help, please and thank you <3

Step-by-step explanation:
The formula of a distance between two points:
[tex]d=\sqrt{(x_2-x_1)^2+(y_2-y_1)^2}[/tex]
We have
A(0, 0), C(a, b)
[tex]AC=\sqrt{(a-0)^2+(b-0)^2=\sqrt{a^2+b^2}[/tex]
B(a, 0), D(0, b)
[tex]BD=\sqrt{(0-a)^2+(b-0)^2}=\sqrt{(-a)^2+b^2}=\sqrt{a^2+b^2}[/tex]
Therefore AC = BD.