已知正項(xiàng)級數(shù)un收斂,試證下列級數(shù)皆收斂:.
已知正項(xiàng)級數(shù)un收斂,試證下列級數(shù)皆收斂:u2n-1.
已知級數(shù)收斂,試證級數(shù)絕對收斂.