Chapter 7 Word formulas

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Chapter 7 Word formulas

Formulas are used a lot in Mathematics.

A formula is a rule that describes how to perform a particular calculation.

7.1 Make a formula from a description

Work out how to calculate something by trying a few times and seeing how you do it.

Put your answers in a table.

S4 on page 229

Homework : exercises 1 t/m 8

7.2 Making a graph from a formula

You first need to make a table

The top row of the table will be the horizontal axis .

and the bottom row will be the vertical axis.

Remember to use equal size steps on both axes.

Fill values from top row into the formula to calculate the values for the bottom row.

Now you have values to plot (draw) your graph.

Formula

Table

Graph

S5 on page 230

Homework: exercises 9 t/m 11

7.3 Linear formulas

Linear sounds like the word line.

In this chapter we are looking at linear graphs which are straight line graphs. 

Every time the same amount is added or subtracted.

Sometimes the straight line goes through (0,0) the origin and sometimes there is a starting amount which means the line starts higher up the vertical axis.

To see if a graph is rising or falling

Rising means going up or getting bigger.

This is when you add an amount every time.

Falling means going down or becoming smaller.

This happens when you take an amount away (subtract) every time.

S6 on page 230

Homework: 17 t/m 24

7.4 Making a Formula from a graph.

You first need to make a table

Then you can see the starting amount and work out how much it increases or decreases every time.

e.g. Amount = starting amount + gradient x time

Gradient = how much goes up/how much across

To see if a graph is rising or falling

S8 on page 231

Homework : ex 25 t/m 31

7.5 Comparing Graphs 

Filling values into formula

If we fill a value into the formula we can calculate the answer.

Sometimes we use this to see if the answer they give is correct.

Sometimes we do it to see if the answer is same as the answer we get from another formula.

e.g To see if point (50,75) is on a line?

Fill value 50 into formula and it should give answer 75.

If it gives a different answer then not on the graph (line).

e.g. To compare two different formulas

Make a table with values.

Underneath calculate the answers using one formula.

Then underneath that calculate the answers using the other formula.

Now you can see when the two answers are equal and/or which one is bigger or smaller for a certain value.

Any questions?