Surds

maddockn

Hi Guys,

can you simplify the following surd, I'm getting a different answer t the reference material

(2+√5)(5-√20)

(edited 13 years ago)

Reply 1

karateworm

11

Oi mate, you looking at my surd?

Reply 2

NubbliNubbleton

8

I thought this was going to be a thread on soapy turds. :rant:

Reply 3

karateworm

11

NubbliNubbleton

I thought this was going to be a thread on soapy turds. :rant:

I just loled... an actual lol! +rep :p:

Reply 4

cambo211

19

maddockn

Hi Guys,

can you simplify the following surd, I'm getting a different answer t the reference material

(2+√5)(5-√20)

I get √5.

Reply 5

JollyJelly

13

OK, I'm probably completely wrong, I've only just finished doing surds and i'm still not 100%
Practice makes perfect though... I get:

10 - 2√20 + 5√5 - 10

OK, that just doesn't look right lol, what does your book give you?

Reply 6

Jambre

9

10 + 5\sqrt5 - 2\sqrt20 -\sqrt80

= 10 + 5\sqrt5 -2\sqrt{4\times5} - \sqrt{16\times5}

= 10 + 5\sqrt5 - 4\sqrt5 -4\sqrt5

= 10 -3\sqrt5

Reply 7

xoxAngel_Kxox

21

This isn't remotely helpful (sorry!) but I used to hate, hate, HATE surds when I had to do them for GCSE :frown:

Reply 8

cambo211

19

Jambre

10 + 5\sqrt5 - 2\sqrt20 -\sqrt80

= 10 + 5\sqrt5 -2\sqrt{4\times5} - \sqrt{16\times5}

= 10 + 5\sqrt5 - 4\sqrt5 -4\sqrt5

= 10 -3\sqrt5

Where does root 80 come from?

root 5 x root 20 = 10

Reply 9

cambo211

19

james-brown28

OK, I'm probably completely wrong, I've only just finished doing surds and i'm still not 100%
Practice makes perfect though... I get:

10 - 2√20 + 5√5 - 10

OK, that just doesn't look right lol, what does your book give you?