the complete question is
What polynomial identity should be used to prove that 21 = 25 − 4
A: Difference of cubes
B: Difference of Squares
C: Square of Binomial
D: Sum of Cubes
we know that
The difference of two squares is a squared number subtracted from another squared number
So
[tex] (a^{2} -b^{2} )=(a+b)*(a-b) [/tex]
In this problem
[tex] 25=5^{2}\\ 4=2^{2}
[/tex]
then
[tex] (5^{2} -2^{2} )=(5+2)*(5-2) [/tex]
[tex] (5^{2} -2^{2} )=(7)*(3) [/tex]
[tex] (5^{2} -2^{2} )=21 [/tex]
[tex] 25-4=21 [/tex]
therefore
the answer is the option
B: Difference of Squares
