Page 13 - 新思维数学活动用书9 样章

2 Expressions and formulae

2 Match each expression, A to F, with the correct value, i to vi, Tip
when a = 8 and b = 4.
Remember, ab
A a + b B a − b C ab D a E b F 2a + b means a × b.
b
a

i 32 ii 1 iii 12 iv 20 v 4 vi 2
2
3 Copy and complete the workings to find the value of each
expression when x = 6 and y = −2. Tip

a x + y = 6 + −2 = − = Remember:
b x − y = 6 − −2 = + = + − → − and − − → +
c x + y = 6 + (−2) = + = So:
2
2
2
2
d 3x + y = 3 × 6 + −2 = − = + −2 is overall −2;
e x + 4y = 6 + 4 × −2 = − = −2 × −2 is overall +4
f 3x + 4y = 3 × 6 + 4 × −2 = − =
4 Work out the value of each expression when a = −3 and b = 5.
a a + b b 3a − b c 20 − ab

d a + 4 e 7b f b − 25
3
2
5
Practice
5 Work out the value of each expression when a = 2, b = −3, c = 4 and d = −5.
a a + 2b b bd − 10 c 4b + 2a

d ab + cd e cd + ab f d 2 − a
2
g 20 − a 3 h bc + d
a
6 This is part of Malik’s homework.

Question
Work out the value of each expression when x = –4
and y = –1.

a xy – 3x b x – x
2
3
2y

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