Question

-49x^2 +16 factor completely

Answer 1

(-7x+4)(7x+4)
-49x^2-28x+28x+16

Answer 2

recognize the difference of 2 perfect squares

remember
a²-b²=(a-b)(a+b)
so

we can rearange them to look like this:
16-49x²
then show the squares
(4)²-(7x)²
then factor
(4-7x)(4+7x)