Page 49 - 新思维数学学生用书7 样章

2 Expressions, formulae and equations

6 This is part of Bethan’s homework. Bethan has made a mistake in

every answer. Explain what Bethan has done wrong. Work out the
correct answers.

Question

Multiply out the brackets.
a 4(x + 4) b 2(6x − 3)

c 3(2 − 5x) d 6(2 − x)

Solution
a 4(x + 4) = 4x + 8 b 2(6x − 3) = 12x – 3

c 3(2 − 5x) = 6 + 15x d 6(2 − x) = 12 − 6x = 6x

Look again at Question 6. What method did you use to answer this question?
Do you think this was the best method or would you use a different method if

you had to answer the question again?

When I
7 Arun looks at these four expressions. expand the brackets
in all of these expressions,
2(12x + 15) 3(10 + 8x) the answers are all the

same.
4(6x + 26) 6(5 + 4x)
Is Arun correct? Explain your answer

and show your working.

Think like a mathematician

8 Discuss with a partner the answers to these questions.
a When you expand the brackets in the expressions 3(4b + 5) and 3(5 + 4b),

do you get the same answer?
b When you expand the brackets in the expressions 2(5c − 1) and 2(1 − 5c),
do you get the same answer?
Give evidence to justify your answers.

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