Monday, 8 June 2009

Meaning of Minus

To the ignorant, a "-" or minus is a strange symbol.

Is this more so when it is expressed as "-6", "-5 km", "-$3", etc.

What is then the true meaning of this "minus" sign?

Answer: It indicates a reversal of action of intention.

Maths is a useful tool to help explain this concept.


When a car moves forward by 5 km, it moves +5 km. ( By default, no sign means positive)
When it reverses by 5 km, it moves -5 km. The direction of movement reverses!

When a person gain $3, he has +$3 in his pocket.
When he loses $3, he has -$3.

From the 2 examples above, you can see that the "minus" sign is a reversal to the default.

If you "reverse" and then "reverse" again, you find yourself in the positive direction.
(-1) x (-1) = + 1

If you reverse 5 times, 5 x (-1) = -5 . You are facing the reverse to the default starting direction.

Now take note of this coming information.
If you reverse the car by 5m and another 5m, you reversed in total (-5) + (-5) = -10m.

If you reverse the car by 5m, followed by changing the direction and moving by another 5m, you moved (-5) + (+5) = 0m.
(Reverse direction followed by forward direction).

Does all these "reversing" cause a daze in you?

Do not despair.
Message is "When there is a reversal, put a minus in front of the number". Simply that!

I owe you $5 ==> -$5.
I gained $5 but lost $3 ==> + $5 + (- $3) = $2 (Action followed by another using "+").


Hope this post on minus sign reduces your anxiety about this little maths symbol.

Cheers :-)



Anonymous said...

This is really basic! Useful for 3 year old boy. Anyway, your website is very interesting and useful! Good Luck.

EeHai said...

Yes, I always believe that in maths learning that mastery of the principles and concepts is still key to solid foundation. Only upon that do we find understanding and application easy and meaning.
Knowing basics is still needed in whatever we learn to avoid a shaky learning journey.