Question

Which shows the expression factored correctly? 16x^2-25

Answer 1

Lets take a look at the options first.
option 1 and option 4 are not possible as (8x) (8x) would give us 64x^2, which is not what we want.

we’re left with option 2 & 3. when expanded, option 2 will look like :
16x^2 - 40x - 10x + 25
= 16x^2 - 50x + 25

however, we do not want the 50x. so the answer is option 3, (4x-5) (4x+5)

if you don’t want to find the answer using expanding, there is also another method of expanding.

(a+b)^2 = a^2 - b^2

in this case, 16x^2 will be a^2 and 25 will be b^2. not sure whether you’ve learn this but yea.