(2x-5y)(x+y)
First you open the brackets by multiplying each term in the first bracket by each term in the second one.
So: (2x-5y) (x+y)
2x2 + 2xy -5xy -5y
Collect like terms. Therefore it becomes: 2x2 -3xy - 5y
So: (2x-5y) (x+y)
2x2 + 2xy -5xy -5y
Collect like terms. Therefore it becomes: 2x2 -3xy - 5y