Saturday, 17 January 2009

Indices | Interesting Mistakes (2)

For maths problem related to indices, you do not only look at the power. You have to take care of the base too.

The common mistake is to ignore the sign of the base when doing computation involving index.

A simple example illustrates the error that is very common when learning maths.

Solve 3x2 - 4x + 1 = 0 using the quadratic formula.

In solving, we need to extract out the a = 3, b= -4 and c = 1 to fill into the quadratic formula.

However, the quadratic formula requires the utilisation of the b2 - 4ac expression.

Here the mistake is to fill in b2 as -42 = - 16!

This shouldn't be the case. It should be (-4)2 = 16.

It is a difference of the sign (positive versus negative).

Thus to handle question on indices, you will have to be extra careful on the base and its sign. Make full use of parentheses, if possible, to group and focus the targeted term or number.

In summary, index or power affects whatever it includes, base and its sign together.

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