=[(a+b+c)+(a-b-c)][(a+b+c)-(a-b-c)]
=2a(2b+2c)
=4a(b+c)
=4ab+4ac
2.x^5-(x^3)(y^2)
=x^3(x^2-y^2)
=x^3(x+y)(x-y)
3.(x^2)(x-y)-(y^2)(x-y)
=(x-y)(x^2-y^2)
=(x-y)(x+y)(x-y)
=(x-y)^2(x+y)
Because x is not equal to y.
So (x-y) 2 > 0.
Because both x and y are positive numbers, x+y >; 0
So (x-y) 2 (x+y) > 0.
(x^2)(x-y)-(y^2)(x-y)>; 0
(x^2)(x-y)>; (y^2)(x-y)
4。 (2x+3y)(2x-3y)= 3 1 = 1 * 3 1
Because x and y are positive integers.
So 2x+3y > 2x-3y, 2x+3y > 0.
So 2x+3y=3 1.
2x-3y= 1
Plus 4x=32
x=8
y=(3 1-2x)/3=5