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```Date: 12/07/2003 at 20:55:16
From: Kristina

I don't understand on how to solve radical equations. Example:
__
\/5x = 1.5

I always seem to lose a step, or skip a step.
```

```
Date: 12/08/2003 at 12:31:11
From: Doctor Riz

Hi Kristina -

Thanks for writing Dr. Math. Radical equations are one of the trickier
things in algebra because they have some subtle points that need to be

The general rule for solving radical equations is to isolate the
radical on one side of the equation, then raise both sides to whatever
power you need to undo or cancel the radical.

For example, if you have a square root, you will square both sides of
the equation.  If you have a cube root, you will cube both sides.

Here's an example:
__
\/x  = 5

Square both sides, and get x = 25.

So in your problem, you have:
__
\/5x  = 1.5

Squaring both sides gives 5x = 2.25, and then you just need to divide
by 5 to find x.

Now, here are the two main subtleties that come into play on radical
equations.  First, when you square both sides, you have to square the
entire side, not piece by piece.  Suppose you have:
_
\/x = x + 2

When you square both sides, you can't just square the x and the 2
separately on the right.  You have to take the whole side and square
it:
_
\/x = x + 2

x = (x + 2)^2

x = x^2 + 4x + 4

Many students make the mistake of just squaring each piece and getting
x^2 + 4 on the right rather than x^2 + 4x + 4.

The second and more common subtlety involves what happens when you
square both sides.  Here's an untrue statement:

-2 = 2

But when I square both sides, that untrue statement becomes:

4 = 4

which is clearly true!  This means that sometimes when you square both
sides of an equation you wind up with answers that don't really check
in the original equation.  Therefore, you ALWAYS have to check your
answer and make sure it works.  Here's an example:
_
\/x = -3

Squaring both sides gives x = 9, but when we check that we have:
_
\/9 = -3

Is that a true statement?  Remember that the square root of 9 could be
3 or -3, but we agree that the way the radical is written will tell us
which one we mean:
_
\/9 = 3
_
-\/9 = -3

So in this example, the answer of 9 does not work because it gives us

3 = -3

when we check it.  That means there is no possible solution to the
given equation.

Confusing?  Sometimes, yes.  The things to remember as you work on

1) Isolate the radical and raise to a power to get rid of it.

2) When you raise to that power, raise both sides of the equation.
You can't do it term-by-term.  Slap ( ) around the other side
of the equation and put the exponent outside the ( ) to remind
you to raise the whole side to that power.

work or be off by a negative, in which case you have to throw
it out.

Hope that helps.  Good luck, and write back if you need more help on
this.

- Doctor Riz, The Math Forum
http://mathforum.org/dr.math/
```
Associated Topics:
High School Square & Cube Roots
Middle School Square Roots

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