Page 12 - 新思维数学活动用书9 样章

2 Expressions and

formulae

2.1 Substituting into expressions

When you substitute numbers into an expression or formula, you must use Key word
the correct order of operations. Work out brackets and indices first, then

divisions and multiplications, and finally additions and subtractions. counter-example

Exercise 2.1

Focus

1 Copy and complete the workings to find the value of each
expression when x = 10. Tips

a 2x + 3 2 × x + 3 = 2 × 10 + 3 a Work out the
= + 3 = multiplication
before the
addition.
b x − 4 x ÷ 2 − 4 = 10 ÷ 2 − 4 b Work out the
2
= − 4 = division before
the subtraction.

c 4x 2 4 × x = 4 × 10 2 c Work out
2
= 4 × = the indices
before the
multiplication.

d 3(x + 2) 3 × (x + 2) = 3 × (10 + 2) d Work out
= 3 × = the bracket

before the
multiplication.

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