a)
[tex](2a+5)(3+b)=6a+2ab+15+5b[/tex]
b)
[tex](a-2b)(5-3a)=5a-3a^{2} -10b+6ab[/tex]
c)
[tex](x-y)(3x+4y)=3x^{2} +4xy-3xy-4y^{2} =3x^{2} +xy-4y^{2}[/tex]
d)
[tex](xy-y)(5xy+3y)=5x^{2} y^{2} +3xy^{2} -5xy^{2} -3y^{2} =5x^{2} y^{2}-2xy^{2} -3y^{2}[/tex]
