Page 40 - 新思维数学学生用书8 样章

2.2 Using expressions and formulae

12 Xavier uses this formula to work out the volume of a triangular prism. Tip
V = bhl where: V is the volume; b is the base; h is the height;
2 Remember that
l is the length.
Xavier compares two prisms. bhl means
Prism A has a base of 8 cm, height of 5 cm and length of 18 cm. b × h × l.
Prism B has a base of 9 cm, height of 14 cm and length of 6 cm.

Xavier works out that Prism A has the larger volume by 12 cm .
3
Is Xavier correct? Explain your answer.

Think like a mathematician

13 Work with a partner to answer this question.
Discuss which answers are correct. Identify the mistakes
that have led to the incorrect answers.
Make x the subject of each formula.
Write which answer is correct, A, B or C. Tip

a y = x + 9 A x = y + 9 B x = y − 9 C x = 9 − y

b y = mx A x = my B x = m C x = y To answer this
y m question, you
c y = x − c A x = y + c B x = y − c C x = c − y will need to

d y = A x = B x = ky C x = k critique the given
y
x
k k y answers and
e y = 7x − 3 A x = y + 3 B x = y + 3 C x = y − 3 improve them.
7 7 7

14 a Use the formula T = mg to work out the value of Tip
T when m = 4.5 and g = 10.
b Rearrange the formula T = mg to make m the subject. Use inverse
c Use your formula to work out the value of m when operations on
T = 320 and g = 10. T = m × g

15 a Use the formula h = k − d to work out the value of h when to make the
k = 72 and d = 37. formula
b Rearrange the formula h = k − d to make k the subject.
c Use your formula to work out the value of k when m =

h = 0.42 and d = 1.83.

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