Answer:
The correct option is 3.
Step-by-step explanation:
The difference of squares is defined as
[tex]a^2-b^2=(a-b)(a+b)[/tex]
In option 1,
[tex](-7x+4)(-7x+4)=(-7x+4)^2[/tex]
This expression is a perfect square, therefore this is not the difference of squares. Option 1 is incorrect.
In option 2,
[tex](-7x+4)(4-7x)=(-7x+4)(-7x+4)=(-7x+4)^2[/tex]
This expression is a perfect square, therefore this is not the difference of squares. Option 2 is incorrect.
In option 3,
[tex](-7x+4)(-7x-4)=(-7x)^2-(4)^2[/tex]
This expression is the difference of squares., therefore Option 3 is correct.
In option 4,
[tex](-7x+4)(7x-4)=-(-7x+4)(-7x+4)=-(-7x+4)^2[/tex]
This expression is a perfect square, therefore this is not the difference of squares. Option 4 is incorrect.