A method to find the law

1. First, list the possible combinations of 1 1 and 9 above:

1) 1 1 + 9 = 20

2) 1 1 - 9 = 2

3) 1 1 × 9 = 99

4) 1 1 ÷ 9 = 1.222

Of course, there are also square roots, sine, cosine and so on. According to the respondents' knowledge range.

2. List the possible combinations of 5 and 4 below.

1)5 + 4 = 9

2)5 - 4 = 1

3)5 × 4 = 20

4) 5 ÷ 4 = 1.25

3. I found that the sum of the additions above the options I want to answer is equal to the product of the multiplications below.

4. Use the rules found in step 3 to test whether the latter two are correct. If established, the law will appear!