Page 37 - 新思维数学学生用书7 样章

2 Expressions, formulae and equations

11 The diagram shows two rectangles.

x cm y cm

length length
The green rectangle on the left has a width of x cm. The length is

six times the width.
The blue rectangle on the right has a width of y cm. The length is
3 cm more than two times the width.
Write an expression for the difference in the lengths of the rectangles.

Summary checklist

I can use letters to represent unknown numbers.
I can use the correct order of operations in algebraic expressions.
I can write and understand expressions.

2.2 Using expressions and formulae

In this section you will … Key words

• substitute numbers into expressions derive

• write and use formulae. formula

formulae
A formula is a mathematical rule that shows the relationship between two

quantities (variables). substitute
You can write a formula using words:
Area of rectangle = length × width or using letters: A = l × w
You can substitute numbers into expressions and formulae.
When l = 5 cm and w = 4 cm, A = 5 × 4 = 20 cm .
2
You can write or derive your own formulae, to help you solve problems.

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