Fix linear equation system solving in Calc (bug#35374)

* lisp/calc/calcalg2.el (math-try-solve-for):
To solve Ax^n=0 where A is a nonzero constant and x the variable to
solve for, solve x^n=0 instead of solving A=0 (which obviously fails)
or something equally stupid.
* test/lisp/calc/calc-tests.el (calc-test-solve-linear-system): New.

1 files changed, 6 insertions, 0 deletions

diff --git a/lisp/calc/calcalg2.el b/lisp/calc/calcalg2.el
index 18243bfc749..2a716633ae6 100644
--- a/lisp/calc/calcalg2.el
+++ b/lisp/calc/calcalg2.el
@@ -2417,6 +2417,12 @@
                             ((= (length math-t1) 2)
                              (apply 'math-solve-linear
                                     (car math-t2) math-try-solve-sign math-t1))
+                            ((= (length math-t1) 1)
+                             ;; Constant polynomial.
+                             (if (eql (nth 2 math-t2) 1)
+                                 nil    ; No possible solution.
+                               ;; Root of the factor, if any.
+                               (math-try-solve-for (nth 2 math-t2) 0 nil t)))
                             (math-solve-full
                              (math-poly-all-roots (car math-t2) math-t1))
                             (calc-symbolic-mode nil)