Find the following products and verify the result for x=-1, y=-2:

(3x – 5y) × (x + y)

= x (3x – 5y) + y (3x – 5y)

= 3x² – 5xy + 3xy – 5y²

= 3x² – 2xy – 5y²

Putting x = - 1 and y = - 2, we have

[3 (-1) – 5 (-2)] [(1) + (-2)] = 3 (-1)² – 2 (-1) (-2) – 5 (-2)²

(-3 + 10) (-1 – 2) = 3 – 4 – 20

- 21 = - 21

Therefore,

L.H.S = R.H.S

Hence, verified