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a surd problem, help please

This is a question half way through a list of surd questions im practising on, I have managed all the rest ok but this one has me stumped.

See the question in link below.

I know the answer is correct from the text book but I can't yet understand how they get it. I know its something embarrassing simple but I cant see it...

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Reply 1

Laz236

If you multiply the 3root2 by 2/2 you end up with (6root2) /2 - (root2)/2. Now you just subtract fractions :biggrin:

Edit: another way to do it could be to factorise the root 2 out of the equation leaving you with root2(3-1/2) and then simply that answer to the correct one.

(edited 9 years ago)

Reply 2

silverpuma

Original post by Laz236

If you multiply the 3root2 by 2/2 you end up with (6root2) /2 - (root2)/2. Now you just subtract fractions :biggrin:

Edit: another way to do it could be to factorise the root 2 out of the equation leaving you with root2(3-1/2) and then simply that answer to the correct one.

Unfortunately I can't follow your explaination. I must be a real dunderhead :frown:

Why would you multiply? And its not an equation its a subtraction problem? I might have to admit defeat here with myself and realise my grey matter (the small amount still left) has hardened.................. :eek:

Reply 3

davros

Original post by silverpuma

Unfortunately I can't follow your explaination. I must be a real dunderhead :frown:

You basically have A - B, where B is a fraction. A doesn't "look like" a fraction so you have to convert it into a fraction with the same denominator as B, hence the multiplication. (Does the phrase "common denominator" ring any bells?)

Reply 4

silverpuma

Original post by davros

My goodness I just smiled and kicked myself. Of course its like screaming at me now how simple this was, I'm amazed how I missed it, but its good for knocking any arrogance out of me..... :smile:

Just equivalent fractions, so common denominators.

I have just sailed through algebraic fractions with common denominators with not too much trouble but it shows me once again how easy it is to make bloopers......on the blooper score I'm a A*** student :colondollar: