Find the points on the lemniscate where the tangent is horizontal

In her article "why should i vote? " stephanie goggin crafts a well-organized and coherent argument. she states that every person of voting age who is registered should vote. she also argues that if you are not registered to vote, you should be. in conclusion, goggin's argument is laid out in a thoughtful and thorough way that is convincing to readers. which element is missing from this evaluation?