The connection FG is also called dq⊥ab. cp⊥ab.

What is the minimum AC+BD? Equivalent to? Ac 2+BD 2 is the lowest?

pythagorean theorem

AC^2+BD^2 = CP^2+AP^2+DQ^2+BQ^2

∫CP and DQ must be

∴ CP 2+DQ 2 required

The minimum value of ∴ac2+bd2 means the minimum value of AP 2+BQ 2.

∫AP+BQ = a b-PQ is a constant value.

When AP=BQ? Minimum value of AP 2+BQ 2