first

Using the property of equal ratio,

There is a formula

2.

If a, b, c and d are geometric series, then it is satisfied.

Ad=bc, so is the proportional line segment.

3.

Suppose that the four line segments in the question (1) are all proportional line segments, which should be A, D, B, C,

That should be enough.

ac=db

4.

Substituting the data, it is found that 3 times 7 is not equal to 4 times 5, and the conclusion that the hypothesis is wrong can be drawn.

5.

It is concluded that the line segments in the result question (1) are out of proportion.

6.

In the same question (2)

ab=cd

satisfy

7.

It can be concluded that the line segment in question (2) is a proportional line segment.