A plant is 4 cm tall and grows 2 cm per week. Write the equation.

Step by step

The question

Question: A plant is 4 cm tall and grows 2 cm per week.

Write the equation.

1 Which depends on which

The height in cm depends on the number of weeks.

So x is the weeks: the input.

y is the height in cm: the output.

2 Rate of change

Rate of change means: how much y changes when x goes up by 1.

Each week, it goes up by 2.

So m is 2.

3 Start value

The start value is y when x is 0.

At the start, with 0 weeks, it is 4.

Careful!

The 2 is per week: it goes with x.

The 4 is only once.

4 Write the equation

A line is y = m x plus b: m is the rate of change, b is the start value.

So the equation is y = 2x + 4.

5 Check

Let's check with 4 weeks: the equation gives 12.

In the story: 4, plus 2, plus 2, plus 2, plus 2: 12.

So the answer is right!

Let's look back.

First: which depends on which.

Then: rate of change.

Then: start value.

Then: write the equation.

Last: check.