data = {{-1, 0.98686}, {-0.9, 1.73109}, {-0.8, 3.01077}, {-0.7,
3.74048}, {-0.6, 4.29188}, {-0.5, 4.933}, {-0.4, 6.00188}, {-0.3,
5.91091}, {-0.2, 6.04255}, {-0.1, 5.81673}, {0, 5.07286}, {0.1,
5.25928}, {0.2, 4.77866}, {0.3, 4.31009}, {0.4, 4.09588}, {0.5,
3.89998}, {0.6, 4.10196}, {0.7, 3.73851}, {0.8, 4.39733}, {0.9,
3.94103}, {1., 4.52398}};
photo1 = FindFormula[data, x, 200, {"Complexity", "Error", "Score"},
TimeConstraint -> 20, PerformanceGoal -> "Quality",
SpecificityGoal -> 1][[-1, 1]]这是第一段有[[-1, 1]]的部分
data = {{-1, 0.98686}, {-0.9, 1.73109}, {-0.8, 3.01077}, {-0.7,
3.74048}, {-0.6, 4.29188}, {-0.5, 4.933}, {-0.4, 6.00188}, {-0.3,
5.91091}, {-0.2, 6.04255}, {-0.1, 5.81673}, {0, 5.07286}, {0.1,
5.25928}, {0.2, 4.77866}, {0.3, 4.31009}, {0.4, 4.09588}, {0.5,
3.89998}, {0.6, 4.10196}, {0.7, 3.73851}, {0.8, 4.39733}, {0.9,
3.94103}, {1., 4.52398}};
photo1 = FindFormula[data, x, 200, {"Complexity", "Error", "Score"},
TimeConstraint -> 20, PerformanceGoal -> "Quality",
SpecificityGoal -> 1]这是没有的部分，这两段代码写出来的结果完全不同，查帮助也没有答案，我想请问吧友们知道这个[[-1, 1]]有什么作用吗

还有就是我查帮助发现FindFormula[data，x，n，｛prop1，prop2……｝]是返回最多n个与属性prop1，prop2等相关联的最佳函数，我尝试将原代码的200改成1后就无法正确输出结果了，请问这个200有什么作用呢

补充一下原题目

取出末尾元素的首个元素，具体可在文档中搜索[[