Page 28 - 新思维数学活动用书8 样章

2.5 Constructing and solving equations

2.5 Constructing and solving equations

Exercise 2.5 Key words

Focus solve

1 Write if each of the following is a formula, an expression or variable
an equation.
a ab + 7c b m = 2b − 3g 2

c 8(x − 8) d 2x + 5 = 13
Remember that: Examples

A formula is a rule that shows the relationship between two F = ma
or more quantities (variables). It must have an equals sign. v = u + 10t
An expression is a statement that involves one or more 3x − 7
variables, but does not have an equals sign. a + 2b
2
An equation contains an unknown number, it must have 3x − 7 = 14
an equals sign, and it can be solved to find the value of the 4 = 6y + 22

unknown number.

Worked example 2.1

You can use a flow chart like this to solve an equation.
Solve 3x + 5 = 17

Answer
3x + 5 = 17 x ×3 +5 17 Reverse the flow chart to work out
the value of x.
12
So x = 4 4 ÷3 –5 17

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