Page 24 - 新思维数学活动用书8 样章

2.3 Expanding brackets

13 This is part of Sofia’s homework.
She has made a mistake in every question.

Question
Expand and simplify each expression.
1. 3(a + 5) – 3(3a + 5)
2. p(4q + r) + q(2r – 4p)
3. 5b(b + 3a) + a(4a + 6b)

Answers
1. 3(a + 5) – 3(3a + 5) = 3a + 15 – 9a – 15 = 6a + 30
2. p(4q + r) + q(2r – 4p) = 4pq + pr + 2qr – 4pq

2
= 3pr + pq = 4p qr
2
3. 5b(b + 3a) + a(4a + 6b) = 5b + 15ab + 4a + 6ab
2
= 4a + 5b + 11ab
2
2
a Explain what she has done wrong.
b Work out the correct answers.

14 Write down and then simplify an expression for
the area of this compound shape.
(2x − 1) cm

5x cm
3x cm

(3x + 4) cm

23