Page 41 - 新思维数学学生用书8 样章

2 Expressions, formulae and equations

w
16 a Use the formula f = to work out the value of f when w = 60 and p = 12.
p
w
b Rearrange the formula f = to make w the subject.
p
c Use your formula to work out the value of w when f = 0.25 and p = 52.
17 Polly and Theo use different methods to work out the answer to a question.
This is what they write.

Question
Use the formula P = 3n + b to work out the value of n when P = 72 and b = 6.

Answers

Polly Theo
Step 1: Make n Step 2: Substitute Step 1: Substitute Step 2: Solve the
the subject of the in the numbers. in the numbers. equation.
formula. n = 72 − 6 P = 3n + b 72 − 6 = 3n
3
P = 3n + b 66 72 = 3n + 6 66 = 3n
P − b = 3n = 3 66 = n
P − b = n = 22 3
3 22 = n
n = P − b n = 22
3

a Look at Polly and Theo’s methods.
Do you understand both methods?
Do you think you would be able to use both methods?
b Which method do you prefer and why?

c Use your preferred method to answer these questions.
i Use the formula H = 6p − k to work out the value of p when H = 40 and k = 14.
ii Use the formula y = mx + 7 to work out the value of m when y = 25 and x = 3.

40