## 字幕列表 影片播放

• - [Instructor] Flynn's sister loaned him some money,

• and he paid her back over time.

• Flynn graphed the relationship between how much time

• had passed, in weeks, since the loan and how much money

• he still owed his sister.

• What feature of the graph represents

• how long it took Flynn to pay back the loan?

• Pause this video, see if you can figure that out.

• All right, now let's go through each of these choices.

• So the first one is the slope.

• So the slope tells us

• how much do we change in the vertical direction

• for any given change in the horizontal direction.

• So for example, if we start from here,

• we can see that if one week goes by,

• we go from one week to two weeks,

• we can see that our loan went down.

• It went from \$15 to \$10.

• So when we had plus one weeks in time,

• our loan went down by \$5.

• And then that happens over the next week.

• And that rate of how quickly the loan is paid,

• that's what the slope tells us.

• And it would be constant over the course

• of the entire time period is what makes this a line,

• is that slope is always going to be constant.

• So the slope is useful for the rate

• at which the loan is being paid back,

• but it's not the clearest way to figure out

• how long it took Flynn to pay back the loan.

• So I would rule that one out.

• The x-intercept, that's where the graph intersects

• the horizontal axis,

• which is often referred to as the x-axis.

• Or another way to think about it,

• that tells us, that says, what is the x-value

• when our vertical value, our y-value, is equal to zero?

• And our y-value is the money owed.

• So it says, hey how much time has passed when we owe,

• when we don't owe any more money

• or when Flynn doesn't owe any more money to his sister?

• Well that's exactly what they're asking for.

• How long did it take Flynn to pay back the loan?

• And that's what that x-intercept tells us.

• It took him four weeks.

• After four weeks, he didn't owe any more money

• to his sister.

• So I like this choice, but let's just review

• the other ones.

• The y-intercept, well that's where the graph

• intersects the y-axis right over there.

• This tells us what's going on at time t equals zero.

• At time t equal zero or time equal zero,

• when the horizontal variable is equal to zero,

• we see that Flynn owes \$20.

• So this one isn't valuable for figuring out when he,

• how long it takes to pay it back.

• This one is useful for figuring out

• how much did he owe initially.

• So we'll rule that one out.

• And we already picked one choice,

• so we can rule out none of the above.

- [Instructor] Flynn's sister loaned him some money,

# 表中的斜率和截距 (Slope and intercept in tables)

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林宜悉 發佈於 2021 年 01 月 14 日