The textbook is intended for preparation for the unified state exam in mathematics of the profile level. The publication includes an analysis of tasks No. 18 (tasks with a parameter), sample solutions and tasks for self-solution. The manual begins with an analysis of simple problems, covering different solution ideas, then more complex problems are considered. The book will help schoolchildren prepare for solving one of the most difficult USE tasks and work out the skill of solving such problems. The manual can be used by teachers to prepare students for the exam in mathematics in the form of the exam, as well as high school students for self-training and self-control.