Oliver Heaviside wrote...
regardez vous sil vou plait this result of multiplying a7by7 matrix by its
MINVERSE "inverse":
....

Don't attempt French (or any language other than English) unless you
spell it correctly.

for this 10 by 10 matrix, the first 7by7 of which was referred to above:
....

You mean the top-left 7-by-7 minor of the 10-by-10 matrix?

Your problem is lack of precision. The values in your matrix span too
many orders of magnitude to calculate the inverse accurately. You need
to rescale in order to reduce the number of orders of magnitude of the
values in the matrix.