(a-b)(a+b)= a^2 - b^2. Explain how this result can be used to develop a fast way of multiplying 95 x 105.

Question

How would I explain this? Thank you! :-)

Answer 1

isn't 95 = 100-5 and
isn't 105 = 100 + 5 ?

so 85x105 = (100-5)(100+5)
= 100^2 - 5^2
both of those I can do in my head.
= ....