The second proportion is true.
[tex]\frac{XY}{AC}=\frac{BC}{YZ}[/tex]Because it's relating the corresponding sides as it should.
Remember that the proportion must be between corresponding sides to be true.
The last proportion is also true.
[tex]\frac{XY}{AC}=\frac{XZ}{AB}[/tex]Because XY and AC are corresponding sides, XZ and AB as well.
