consider the number 987654321 the sum of the digits is 45.
consider the number 123456789 the sum of the digits is 45.
now subtract 123456789 from 987654321 you get 864197532 the sum of the digits is 45.
Hence 45 - 45 = 45.
Solution:
a = b (then multiply the equation by a)
a^2 = ab (then subtract it by b^2)
a^2 - b^2 = ab - b^2 (then simplify)
(a-b)(a+b) = b(a-b)
a+b = b
a=b-b (then substitute values)
45=45-45