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We know that (x+y)(x−y)=x²−xy+xy−y² (by multiplying out the brackets).
But this is the same as x²−y². So whenever we have an expression like x²−y² we can write it as (x+y)(x-y). This result is often useful for simplifying algebra; it is called the difference of two squares.
For example: 6²−5²=(6+5)(6−5)=11 ×1 = 11.
17²−15²=(17+15)(17−15)=32 ×1 = 64.