Answer:
Option D is correct.
Step-by-step explanation:
In order to simplify the given expression we should know what Distributive property of number is.
It is given by a*x (b-c ) = axb -axc
that is if a is outside of the parenthesis then a is multiplied to all the term inside one by one
here in the question outside is [tex]3x^2[/tex] and inside is [tex]7x^2[/tex] and 9.
therefore [tex]3x^2[/tex] is multiplied to both [tex]7x^2[/tex] and 9
So first term is obtained by multiplying [tex]3x^2[/tex] by [tex]7x^2[/tex] which gives
[tex]21x^4[/tex]
and second term is obtained by multiplying [tex]3x^2[/tex] by 9 we get
[tex]27x^2[/tex]
So expression is [tex]21x^4[/tex]- [tex]27x^2[/tex]
