User blog comment:Explorer 767/One Equals One Hundred/@comment-1024726-20091228001753

Given that $$a = b$$, it can be proven that $$\pi = 3$$.

$$\pi a = \pi b$$ (remember, pi is a constant and can be a coefficient)

$$3a = 3b$$

$$\pi a^2 = \pi ab$$ (multiplying  by  $$a$$)

$$3ab = 3b^2$$  (multiplying  by  $$b$$)

$$\pi a^2-3ab = \pi ab-3b^2$$  (combining  equations)

$$\pi a^2-\pi ab = 3ab-3b^2$$  (subtracting  $$\pi$$ and adding $$3ab$$)

$$\pi a^2-\pi ab + ab - b^2 = 4ab-4b^2$$  (adding  $$ab$$ and subtracting  $$b^2$$)

$$\pi a(a-b) + b(a-b) = 4b(a-b)$$  (factoring)

$$\pi a + b = 4b$$  (dividing  out  $$a-b$$)

$$\pi a = 3b$$  (subtracting  $$b$$)

$$\pi = 3$$  (dividing  by  $$a$$ and $$b$$)

$$Q.E.D.$$

There. No need to memorize anymore.