Some maths problem

1. Sep 6, 2005

IB

Suppose I have sqrt (a^2 - a [delta] d). What do I do? Do I do like this: sqrt (a^2 - a [delta] d) = a - sqrt(a [delta] d)? Thanks.

PS: One more thing. How to write mathematics with latex?

2. Sep 6, 2005

Learning Curve

What is sqrt (a^2 - a [delta] d) equal to? or are you asking to simplify it?

3. Sep 6, 2005

IB

Yeah. I was just wondering whether it can still be simplified.

4. Sep 6, 2005

Hurkyl

Staff Emeritus
Depending on what you want to do, a differential approximation, or maybe a Taylor sum, might be useful.

But as for algebraic manipulation, what you did is wrong. roots and exponents (usually) distribute over multiplication (and division), not addition (and subtraction).

5. Sep 6, 2005

IB

Could you give an example to demonstrate that? And how can I correct my wrong algebraic manipulation? Thanks.

6. Sep 6, 2005

7. Sep 7, 2005

VietDao29

Say a = 5, and delta d = 9 / 5.
So:
$$\sqrt{a ^ 2 - a \Delta d} = \sqrt{5 ^ 2 - 5 \times \frac{9}{5}} = \sqrt{25 - 9} = \sqrt{16} = 4$$
And:
$$a - \sqrt{a \Delta d} = 5 - \sqrt{5 \times \frac{9}{5}} = 5 - \sqrt{9} = 5 - 3 = 2$$
And 4 is not 2.
Viet Dao,

8. Sep 7, 2005

IB

Thanks, VietDao29.