dc: add page

pages/common/dc.md

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+# dc
+
+> An arbitrary precision calculator. Uses reverse polish notation (RPN).
+
+- Run calculator in interactive mode:
+
+`dc`
+
+- Calculate 4 times 5 [4 5 *] subtract 17 [17 -] and [p]rint the output :
+
+`echo "4 5 * 17 - p"| dc`
+
+- Set number of decimal places to 10 [k 7], calculate 5 divided by -3 [5 _3 /] and [p]rint:
+
+`echo "7 k 5 _3 / p" | dc`
+
+- To 100 decimal places [100 k] , calculate the golden ratio, phi, sqrt(5) [5 v] plus 1 [1 +], divided by 2 [2 /] and [p]rint result:
+
+`echo "100 k 5 v 1 + 2 / p" | dc`