Final answer:
Hermione obtained the hair she used in her glass of Polyjuice Potion by using the Hair-Raising Potion.
Step-by-step explanation:
In the Harry Potter series by J.K. Rowling, the Polyjuice Potion is a magical potion that allows the drinker to temporarily assume the physical appearance of another person. The potion is complex and requires several rare ingredients, including a piece of the person whose appearance is to be taken.
Hermione obtained the hair she used in her glass of Polyjuice Potion by using the Hair-Raising Potion. In Harry Potter and the Chamber of Secrets, Hermione brews this potion with the help of a book called Moste Potente Potions. By brewing the Hair-Raising Potion, her hair grows and she is able to collect it for later use in the Polyjuice Potion.