Math...因式分解下列各式....~

No steps can be given, if needed, think it from cross method...
1) x² - 3xy - 40y²
=(x - 8y)(x + 5y)

2) 8x² + 21xy + 10y²
=(8x + 5y)(x + 2y)

3) 6a² - 17ab + 7b²
=(3a - 7b)(2a - b)

4) 20a² - 13ab - 72b²
=(4a - 9b)(5a + 8b)

5) 21p² + 50pq + 24q²
=(3p + 2q)(7p + 12q)

6) 90m² - 4mn - 16n²
=(9m - 4n)(10m + 4n)

7) 2x² + 7xyz - 15y²z²
=(2x - 3yz)(x + 5yz)

8) 9a²b² - 19abc + 10c²
=(9ab - 10c)(ab - c)

9) (3x²)² - 40x² +16
=9(x²)² - 40x² +16
=(9x² - 4)(x² - 4)

10) (6x²)² - 77x²y² - (3y²)²
=36(x²)² - 77x²y² - 9(y²)²
=(9x² + y²)(4x² - 9y²)

唔駛咁灰心...呢d話易唔易~話難唔難~你識做一題就識做其他ga喇~~越做得多越識做~
步驟不外乎因式分解~交叉相乘~確認~組合~
係因式分解o個度要靠估~所以較難~但係做得多就好容易諗到~
第一題可以做示範~

1) x² - 3xy - 40y²

x² - 40y²(以下是因式分解)
--------------
x \ / -8y
x / \ +5y
--------------
-8xy +5xy <---(這裡是交叉相乘)
= -3xy <---(與方程中的"- 3xy"符合)
所以答案是( x - 8y ) ( x + 5y )//

2) 8x² + 21xy + 10y²

8x² + 10y²
--------------------
8x +5y
x +2y
------------------
+5xy +16xy= +21xy <---(與方程中的"+21xy"符合)
所以答案是( 8x + 5y ) ( x + 2y )//

到到呢度~開始明點做未啊??

3) 6a² - 17ab + 7b²

6a² + 7b²
---------------------
3a - 7b
2a - b
--------------------
-14ab -3ab = -17ab
所以答案是 ( 3a - 7b ) ( 2a - b )//

4) 20a² - 13ab - 72b²

20a² - 72b²
--------------------------
4a -9b
5a +8b
-----------------------
-45ab +32ab = - 13ab
所以答案是( 4a - 9b ) ( 5a + 8b )//

5) 21p² + 50pq + 24q²

21p² + 24q²
------------------------------
3p + 2q
7p +12q
--------------------------------
+14pq +36pq
所以答案是( 3p + 2q ) ( 7p + 12q )//

6) 90m² - 4mn - 16n²

90m² - 16n²
-----------------------
10m +4n
9m -4n
-------------------------
+36mn -40mn = -4mn
所以, 90m² - 4mn - 16n² = ( 10m + 4n ) ( 9m - 4n )//

7) 2x² + 7xyz - 15y²z²

2x² - 15y²z²
-------------------------
2x -3yz
x +5yz
-------------------------
-3xyz +10xyz = +7xyz

所以, 2x² + 7xyz - 15y²z² = ( 2x -3yz ) ( x + 5yz )//

8) 9a²b² - 19abc + 10c² ( 呢題易d~因為9同10可以好易聯想到19 [9+10=19] )

9a²b² + 10c²
---------------------------
9ab - 10c
ab - c
---------------------------
-10abc -9abc = - 19abc

所以, 9a²b² - 19abc + 10c² = ( 9ab - 10ca ) ( b - c )//

9) (3x²)² - 40x² +16 [唔好俾d括孤嚇到,(3x²)² = 3x² x 3x², 可以變成9x² x x² ~ )

(3x²)² +16
------------------------
9x² -4
x² -4
--------------------------
-4x² -36x² = -40x²

(3x²)² - 40x² +16 =( 9x² -4) (x² -4)//

10) (6x²)² - 77x²y² - (3y²)²

(6x²)² - (3y²)²
---------------------------
4x² -9y²
9x² +y²
------------------------------
-81x²y² +4x²y² = - 77x²y²
(6x²)² - 77x²y² - (3y²)² = (4x² -9y²)(9x² +y²)//

解到呢度你應該掌握到好多ga喇~~有唔明就msn我la~
[email protected]

1. x² - 3xy - 40y²
(x - 8y)(x + 5y)

2. 8x² + 21xy + 10y²
(8x + 5y)(x + 2y)

3. 6a² - 17ab + 7b²
(3a - 7b)(2a - b)

4. 20a² - 13ab - 72b²
(4a - 9b)(5a + 8b)

5. 21p² + 50pq + 24q²
(3p + 2q)(7p + 12q)

6. 90m² - 4mn - 16n²
(9m - 4n)(10m + 4n)

7. 2x² + 7xyz - 15y²z²
(2x - 3yz)(x + 5yz)

8. 9a²b² - 19abc + 10c²
(9ab - 10c)(ab - c)

9. (3x²)² - 40x² +16
=9(x²)² - 40x² +16
(9x² - 4)(x² - 4)

10. (6x²)² - 77x²y² - (3y²)²
=36(x²)² - 77x²y² - 9(y²)²
(9x² + y²)(4x² - 9y²)

1) (x-8y)(x+5y)