Multiplying polynomials

Question

Can someone help me understand how to multiply polynomials like these:

5mn(7m-2n)

and

3x(x+9)

Answer 1

1) given expression is 5mn(7m-2n)

= 5mn*7m+5mn*2n

= 35m^2n-10mn^2

2) given expression is 3x(x+9)

= 3x*x+3x*9

= 3x^2+27x

Comments

The expression is 5mn(7m - 2n).

Apply distributive property : a(b - c) = ab - ac.

= (5mn * 7m) - (5mn * 2n)

= 35m²n - 10mn² .