what is sin to the negative 1st 3/7

Use the calculator at this site.

First, make certain that you are in the correct mode (lower left-hand corner), either radian or degree.

Then press (2nd) key.

Then press (asin) key.      "asin"  is "arcsin"  which is "invsin"

Enter 3/7 and press (=).

The answer is approximately 25 degrees.