Problems encountered in the use of router-link exact

<router-link :to=""/detail/"+userID+"/"+id" class="peertab" active-class="isactive"></router-link>
<router-link :to=""/detail/"+userID+"/"+id +"/task""class="peertab" active-class="isactive"></router-link>

<a  href="-sharp/detail/3891330/6763" class="peertab isactive"></a>
<a  href="-sharp/detail/3891330/6763/task" class="peertab isactive"></a>

add exact to router-link and find that if active-class is not shown to be removed, the first one always retains active-class. Why?
do I think the corresponding is correct

Mar.03,2021
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