In the triangle ABC, AB equals 5, AC equals 7, ad is the middle line on the side of BC, then the range of ad is?

In the triangle ABC, AB equals 5, AC equals 7, ad is the middle line on the side of BC, then the range of ad is?

Extend the middle line to point E, connect be, make be parallel to ac. so 5,7,2ad form a triangle, so 1