There is a bird flying from the top of a small tree to the top of a big tree. What is the shortest distance he flies?

Analysis: Draw a figure according to the meaning of the question, construct a right triangle and solve it with Pythagorean theorem.

Solution: As shown in the figure, point D is DE⊥AB, and the vertical foot is E.

∫AB = 13，CD=8

And ∵BE=CD, DE=BC.

∴AE=AB-BE=AB-CD= 13-8=5

In Rt△ADE, DE=BC= 12.

∴ad2=ae2+de2= 122+52= 144+25= 169

∴AD= 13 (negative values are rounded off)

Answer: The shortest flying distance of a bird is 13m. ..