题目

The right to vote is one of the most fundamental rights of any democracy. Yet, for too long, too many of our fellow citizens were denied that right simply because of the color of their skin. Fifty years ago this week, President Lyndon Johnson signed a law to change that. The Voting Rights Act broke down legal barriers that stood between millions of African Americans and their constitutional right to cast ballot(投票). It was, and still is, one of the greatest victories in our country’s struggle for civil rights. But it didn’t happen overnight. Countless men and women marched and 两个力F1，F2的夹角为60°，且大小都是10 N，则它们的合力F的大小是________．