Many sailors use calculations for

boat ratios, perhaps

rigging, or

navigation.

So, this should be easy right?

Here's a mathematical proof that appears to show that 2=1. Can you find what's wrong with it.

Let x=y

Then x^2=xy (by multiplying both sides by x)

Then x^2-y^2=xy-y^2 (by subtracting y^2 from both sides)

Then (x+y)(x-y)=y(x-y) (by factoring both sides)

Then x+y=y (by dividing both sides by (x-y))

Then y+y=y (since x=y by the original assumption)

ie. 2y=y

Therefore 2=1 (by dividing both sides by y)

Clearly 2 and 1 are not equal, what mistake was made above?