中2 maths question !!!!!

1. 6x - 6a + xy -ay
=6(x-a)+y(x-a)
=(6+y)(x-a)


2. The size of each interior angle (A) of a reregular polygon can be calculated by the following formula:

A: (n-2x180/n) where n is the number of sides of the polygon.

(a) Find the size of an interior angle of a regular 10-sided polygon
(10-2)*180/10
=8*180/10
=144

(b) If the size of a regular polygon is 172, find the number of sides of the polygon.
(n-2)*180/n=172
180n-360=172n
8n=360
n=45

Expand the following question

3. (2b+1)(2b-1)
=(2b)^2-1^2
=4b^2-1

4. 2(3p+4)(3p-4)
=2(9p^2-16) 做法同上面果條一樣
=18p^2-32

5. -3(8s+3r)(3r+8s)
=-3[(8s)^2+2(8s)(3r)+(3r)^2] 因為(a+b)^2=a^2+2ab+b^2
=-3(64s^2+48sr+9r^2)
=-192s^2-144sr-27r^2

6. (7a+9b)(右上角有小2字) 就像(......)^ 的^一樣
=49a^2+126ab+81b^2 做法同上面果條一樣

7.(4a-7b)^
=16a^2-56ab+49b^2 因為(a-b)^2=a^2-2ab+b^2

8.(3a-2b)(-2b-3a)
=-(3a-2b)(2b+3a)
=-9a^2+4b^2

1. 6x - 6a + xy -ay
= 6(x-a) + y(x-a)
= (x-a)(6-a)

2. (a) Given that A: [(n-2)180]/n
Sub, n=10,
A=[(10-2)180]/10
A= 144

(b) When A=172,
[(n-2)180]/n = 172
180n -360 = 172n
n=25

(3) (2b+1)(2b-1)
= 4b^2-2b+2b-1
=4b^2-1

4. 2(3p+4)(3p-4)
= (6p+12)(3p-4)
=18p^2-24p+36p-36
=18p^2-12p-26
=6(3p^2-2p-6)

5. -3(8s+3r)(3r+8s)
=(-24rs-9r)(3r+8s)
=-72rs-27r^2-192s^2-72sr
=-(27r^2+144rs+192s^2)

6. (7a+9b)(右上角有小2字) 就像(......)^ 的^一樣
=49a^2+126ab+81b^2

7.(4a-7b)^2
=16a^2-63ab+49b^2

8.(3a-2b)(-2b-3a)
=-6ab-9a^2+4b^2+6ab
-(9a^2-4b^2)