mathematics
posted by STACEY .
Factorise copletely
1) 2ax+3ay2bx3by
2)5x^220
3)3x^2+4x15 is the ans to this one = 7x^315

You mean factor
a(2x+3y)b(2x+3y)
= (ab)(2x+3y)
5(x^24)
= 5 (x2)(x+2)
(3x5)(x+3) 
first one is "grouping"
2ax+3ay2bx3by
= a(2x+3y)  b(2x+3y)
= (2x+3y)(ab)
second, common factor then difference of squares
5x^220
= 5(x^2  4)
= 5(x+2)(x2)
third, general quadratic
3x^2+4x15
= (3x5)(x+3)
looks like you got your answer by
adding 3x^2 + 4x to get 7x^3
that is just unforgivable!