Page 26 - 新思维数学学生用书9 样章

2.2 Constructing expressions

10 Show that 5a − 9 b − a + 2 + 7ab = −5a − 6a 3 − ab) 4 + 9 when a = −2 and b = −1.
(
2
)
(
b 5 b b 2 − a 3
Look back at the questions in this exercise.

• Which questions did you find easy to answer? Why?
• Which questions did you find difficult to answer? Why?
• Do you feel confident using the correct order of operations?

• Do you feel confident substituting negative numbers into
expressions?
• What can you do to improve your skills in this topic?

Summary checklist

I can use the correct order of operations in algebraic expressions.

2.2 Constructing expressions

In this section you will … Key word

• use letters to represent numbers in terms of
• use the correct order of operations in algebraic
expressions.

In algebraic expressions, letters represent unknown numbers. You often need to construct algebraic
expressions to help you solve problems. Suppose you want to work out the price of tickets for a day
out. You might choose to let a represent the price of an adult’s ticket and c represent the price of a

child’s ticket.
• You can write the total price for an adult’s ticket and a child’s ticket as a + c.
• You can write the difference between the price of an adult’s ticket and a child’s ticket as a − c.
• You can write the total price of tickets for 2 adults and 2 children as 2(a + c) or 2a + 2c.

These expressions are written in terms of a and c.

25