5: \(=4b^2-2b+\dfrac{1}{4}-\dfrac{1}{4}+a-a^2\)

\(=\left(2b\right)^2-2\cdot2b\cdot\dfrac{1}{2}+\left(\dfrac{1}{2}\right)^2-\left(a^2-a+\dfrac{1}{4}\right)\)

\(=\left(2b-\dfrac{1}{2}\right)^2-\left(a-\dfrac{1}{2}\right)^2\)

\(=\left(2b-\dfrac{1}{2}-a+\dfrac{1}{2}\right)\left(2b-\dfrac{1}{2}+a-\dfrac{1}{2}\right)\)

\(=\left(2b-a\right)\left(2b+a-1\right)\)

6:

\(=b^2-4b+4-9c^2\)

\(=\left(b-2\right)^2-9c^2\)

\(=\left(b-2-3c\right)\left(b-2+3c\right)\)

5) \(4b^2-2b+a-a^2\)

\(=\left(2b-a\right)\left(2b+a\right)-\left(2b-a\right)\)

\(=\left(2b-a\right)\left(2b+a-1\right)\)

6) \(b^2-9c^2+4+4b\)

\(=\left(b+2\right)^2-9c^2\)

\(=\left(b+3c+2\right)\left(b-3c+2\right)\)

Part 1:

1. with

2. does

3. after

4. if

5. where

6. I won't

Part 2:

1B 2F 3A 4E 5C 6D

Part 3:

1. invited

2. will play

3. have just won

4. be cleaned

5. to take

6. beautifully

7. impression

Part 4:

1. read -> reading

2. disappointing -> disappointed

3. environment -> environmental

4. who -> that

Part 5:

1. the bad weather

2. are made to study

3. were good at learning

4. going to the English

{ (998-2):2+1 } . (998+2):2

\(=\left(998+2\right)\left[\left(998-2\right):2+1\right]=1000\cdot499=499000\)

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