Explaining the transitive property (of equality) to students this semester without outright telling them what to do:
y = 2*x^2 - 4
y = x^2 - 4*x + 1
IF a = b
AND a = c
THEN b = c
They failed to understand this...so,
IF 10 pennies = 2 nickels
AND 10 pennies = 1 dime
THEN 2 nickels = 1 dime
Some failed to understand this too...so,
IF 10 = 5 + 5
AND 10 = 2*5
THEN 5 + 5 = 2*5
Again, some failed to understand.
>_<