sysvar: fix wrong variables names

system-variables.md

@@ -2398,7 +2398,7 @@ For a system upgraded to v5.0 from an earlier version, if you have not modified
 - This variable is used to set whether the optimizer executes the optimization operation of pushing down the aggregate function to the position before Join, Projection, and UnionAll.
 - When the aggregate operation is slow in query, you can set the variable value to ON.
 
-### tidb_opt_cartesian_bcj
+### tidb_opt_broadcast_cartesian_join
 
 - Scope: SESSION | GLOBAL
 - Persists to cluster: Yes
@@ -2418,7 +2418,7 @@ For a system upgraded to v5.0 from an earlier version, if you have not modified
 - Default value: `3.0`
 - Indicates the CPU cost of starting a Golang goroutine in TiDB. This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.
 
-### tidb_opt_cop_cpu_factor
+### tidb_opt_copcpu_factor
 
 - Scope: SESSION | GLOBAL
 - Persists to cluster: Yes
@@ -2458,7 +2458,7 @@ For a system upgraded to v5.0 from an earlier version, if you have not modified
 - Default value: `3.0`
 - Indicates the CPU cost for TiDB to process one row. This variable is internally used in the [Cost Model](/cost-model.md), and it is **NOT** recommended to modify its value.
 
-### tidb_opt_desc_scan_factor
+### tidb_opt_desc_factor
 
 - Scope: SESSION | GLOBAL
 - Persists to cluster: Yes