Answer:
Explanation:
Let's start by defining a coordinate system where the horizontal axis represents the number of weeks that Gildong has been saving (and spending), and the vertical axis represents the amount of money he has in savings.
During the first 15 weeks, Gildong saved 20,000 won per week, so his savings increased linearly from week 0 to week 15. We can represent this with the equation:
y = 20,000x
where x is the number of weeks since the beginning (x = 0 corresponds to the start of the saving period) and y is the amount of money Gildong has saved after x weeks.
During the next 15 weeks, Gildong spent 20,000 won per week on eating Maratang, so his savings decreased linearly from week 15 to week 30. We can represent this with the equation:
y = -20,000(x - 15) + 20,000(15)
where x is the number of weeks since the beginning (x = 15 corresponds to the start of the spending period) and y is the amount of money Gildong has saved after x weeks.
To represent the total amount of money Gildong had in savings at any given time, we can combine the two equations above using an absolute value:
y = |20,000x| - 20,000(x - 15)
where x is the number of weeks since the beginning, and y is the amount of money Gildong has in savings after x weeks.
This function represents the absolute value of the difference between the amount of money Gildong has saved and the amount of money he has spent on Maratang, taking into account the fact that his savings increased linearly during the first 15 weeks and decreased linearly during the next 15 weeks.