幫幫手,4題數學題

1.(2a+b)² -(a-b)²
=[(2a+b)+(a-b)][(2a+b)-(a-b)]
=(2a+b+a-b)(2a+b-a+b)
=3a(a+2b)

2.(2x+y)² -(x+2y)²
=[(2x+y)+(x+2y)][(2x+y)-(x+2y)]
=(2x+y+x+2y)(2x+y-x-2y)
=(3x+3y)(x-y)
=3(x+y)(x-y)

3. given s=ab/a+b.find the value of b when s=2/3 a=1/2

s=ab/a+b
2/3 = (1/2)b／(1/2)+b
2[(1/2)+b] = (b/2)3
1+2b = 3b/2
2+4b = 3b
2=-b
b=-2

4.1/a-1/x-b=1y
1-a/x-b=ay
x-b-a=ay(x-b)
x-b-a=axy-abx
x-b-a-axy+aby=0
x(1-ay)-b(1-ay)-a=0
(1-ay)(x-b)-a=0
呢條唔多清楚你想問咩...只係盡我能力.....

1. =(2a+b+a-b)(2a+b-a+b)
=3a(a+2b)

2. =(2x+y+x+2y)(2x+y-x-2y)
=(3x+3y)(x-y)
=3(x+y)(x-y)

3.b=-2

4.

2)
(2x+y)² -(x+2y)²
= (2x² + 4xy + y² ) - (x² + 4xy + 2y² )
= 2x² + 4xy + y² - x² - 4xy - 2y²
= x² + 3y²
= (x-3y)(x+3y)
= 3(x-y)(x+y)

(2a+b)2-(a-b)
=4a+b2-a+b
=3a+b3

(2xy)2-(x+2y)2
=(4x2y2)-(x2+4y2)
=4x2y2-x2-4y2
=3x-2y

other i dunno