• 2022-06-03
    用向量证明三角形余弦定理,即[tex=3.143x1.214]BypMH6cWAb0x8gikbHmOkm8G6z9CQ+Rgr92Svssi5/0=[/tex] 中,[p=align:center][tex=8.786x1.357]prvj+IFaklHCGrYlQojp2WnoxpcgipC9Knnh3MjYQ0cwRelnVJOj6If5HI5yH3IC[/tex]此处 [tex=2.286x1.214]/Uu9jgxB4g+DifSL38NMLQ==[/tex]是[tex=5.286x1.214]6gX0sYVht5wbZ0mxG1ai4TvaUgGxUB2vZaAPAKTTIBw=[/tex] 对边的边长(如图)[img=231x183]178e9f3eb273cb1.png[/img]
  • 证 因为[tex=6.571x1.857]nTauydNa/9hor+dUdkGtGqYVhSSj2iHJhCxQN+8y+MYs/Gzdkbs94F6mMLmDgHRVBtxjsxbYHrHYA0/I6Fu/AyAJPOD37Qu9sZ69pJGNsvk=[/tex] 所以[tex=13.429x4.5]ifE9NWj3X6IpRVSt3T5ITrj7xY/lQnc/5gNjK4JUkIpqIgLQklKnkOxkvDPruIehrLHSYMKMzecw/tIEBZ7DqR0SwI9fIJrJ2O1yNJbuDo5F3RoFm1k0EnHbPGqsYdbxJeJkz/+LXKr9Alye4mh1T1LSMXlNxES872hgy5mJJdFinzqcaiMiELgEfX/8JJIBCRbMbGo9MukSXU9PERGKjU68Uf0qb7s7YfAqEEYaQspYPfdV9Dnbutr8tAji+V2uuCaRwBJdha+FnTPXEta8ZwhSHODbETwVg3/FfFpTDAg=[/tex]即[p=align:center][tex=21.357x1.929]mRE03PZsZRFzcKXulfcxEAGanpn6K/4JaljjpjY/EXoRTCMV70A2/niQ00kf2NIQZbxsYrYygAY/6M6ATCRyCRoTMIcrpe25yVIP5tXimdQQezfkH0HbI444/XGzFPIug3hjXagLbppkUd8PSvQWSMwan5JjkKphnif9AjU1NjrIDNGW9v+YLaJ1nQ1NUBwWGt4RMLmm4QpNc20nRlt4vo0VqbYdtQIqUNyCVlixBrie0ykX9fgLuukmlP9CZYm9[/tex]已知[tex=20.286x1.929]mRE03PZsZRFzcKXulfcxEFNd04hTSY+Z1TbAs/Vrb/TdIjAMj2AZ/dyx0R7xKhyz0jmKa9Xw883vfWGliTG93E8WdMi+aW3TbX/SJBWdxYUw9WIQBtmBi/IGtxufq8k36ORG7DHLovN/qM0nqVEbr93n9JMczFALBrhzaYsCs6k9f/N7vjov+FgKIdtFlPMj[/tex]代入上式得[p=align:center][tex=9.071x1.357]prvj+IFaklHCGrYlQojp2Xvy7pnqfGNChHjJK4Bz3muT2IdsJTrtQRiQYQ0htmmt[/tex]

    内容

    • 0

      下面是图的拓扑排序的是?(多选)[img=340x240]1802faef6ebcc2a.png[/img] A: 2 8 0 7 1 3 5 6 4 9 10 11 12 B: 2 8 7 0 6 9 11 12 10 1 3 5 4 C: 8 2 7 3 0 6 1 5 4 9 10 11 12 D: 8 2 7 0 6 9 10 11 12 1 3 5 4

    • 1

      ‌下面说法错误的是( )。‌‌知识点:列表推导式‌ A: dict([(x, x**2) for x in range(6)]) 创建的字典是{0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25} B: [[x*3+y for y in range(1,4)] for x in range(3)] 创建的是二维列表 [[1, 2, 3], [4, 5, 6], [7, 8, 9]] C: number = [-2, 4, 6, -5]string = 'ab'z = [(i, j) if i>0 else (-i, j) for i in number for j in string]这段代码创建的列表为[(2, 'a'), (2, 'b'), (4, 'a'), (4, 'b'), (6, 'a'), (6, 'b'), (5, 'a'), (5, 'b')] D: ' '.join([i for i in range(1,11)])的运算结果为字符串'1 2 3 4 5 6 7 8 9 10'

    • 2

      采用基2频率抽取FFT算法计算点序列的DFT,以下()流图是对的。 A: x[0],x[1],x[2],x[3],x[4],x[5],x[6],x[7] B: x[0],x[2],x[4],x[6],x[1],x[3],x[5],x[7] C: x[0],x[2],x[1],x[3],x[4],x[6],x[5],x[7] D: x[0],x[4],x[2],x[6],x[1],x[5],x[3],x[7]

    • 3

      采用基2时间抽取FFT算法流图计算8点序列的DFT,第一级的数据顺序为 A: x[0],x[2],x[4],x[6],x[1],x[3],x[5],x[7] B: x[0],x[1],x[2],x[3],x[4],x[5],x[6],x[7] C: x[0],x[4],x[2],x[6],x[1],x[5],x[3],x[7] D: x[0],x[2],x[1],x[3],x[4],x[6],x[5],x[7]

    • 4

      若要将一个长度为N=16的序列x(n)重新位倒序,作为某一FFT算法的输入,则位倒序后序列的样本序号为( )。 A: x(15), x(14), x(13), x(12), x(11), x(10), x(9), x(8), x(7), x(6),<br/>x(5), x(4), x(3), x(2), x(1), x(0) B: x(0), x(4), x(2), x(6), x(1), x(5), x(3), x(7), x(8), x(12), x(10),<br/>x(14), x(9), x(13), x(11), x(15) C: x(0), x(2), x(4), x(6), x(8), x(10), x(12), x(14), x(1), x(3), x(5),<br/>x(7), x(9), x(11), x(13), x(15) D: x(0), x(8), x(4), x(12), x(2), x(10), x(6), x(14), x(1), x(9), x(5),<br/>x(13), x(3), x(11), x(7), x(15)