How do you factorise x^2-11

Maya memsaab

14

All help is appreciated

you cant technically factorise it, but you can do (x+root11)(x-root11)

Reply 2

Notnek

21

Original post by Mayavalentine

All help is appreciated

What was the original question? Why do you want to factorise this?

(x+root11)(x-root11)

Original post by Mayavalentine

All help is appreciated

Difference of 2 squares, in the form:
(x+a)(x-a).
The x co-efficient will be 0, just like in your equation.
You can substitute the values of a in to make it work for your equation :smile:

Reply 5

Shibu the Doge

22

(x²-11) = (x-√ 11)(x+√11)

Reply 6

Notnek

21

At GCSE, you would say that e.g.

x^2-2x-4

"doesn't factorise" even though you can write it as

(x-1-\sqrt{5})(x-1+\sqrt{5})

This is why I'm wondering what the original question was.

Reply 7

Maya memsaab

OP

14

Original post by Bathila

(x²-11) = (x-√ 11)(x+√11)

Thanks! How do you know it will be a square root,there's an example in the book which says x^2-5 is (x+sq.root5) (x-sq.root5)

Is always square root with numbers less than 20 or something? I'm not good at maths so sorry for the dumb question!

Reply 8

Loci Pi

16

Original post by Mayavalentine

Thanks! How do you know it will be a square root,there's an example in the book which says x^2-5 is (x+sq.root5) (x-sq.root5)

Is always square root with numbers less than 20 or something? I'm not good at maths so sorry for the dumb question!

If the number added on the the x^2 is a square number, the number in the brackets will be a whole number. If number added isn't a square number, there will be square roots inside the brackets.

The method you're using, difference of 2 squares, basically means
x^2-a^2 = (x+a)(x-a)

(edited 6 years ago)

Reply 9

Shibu the Doge

22

Original post by Mayavalentine

Thanks! How do you know it will be a square root,there's an example in the book which says x^2-5 is (x+sq.root5) (x-sq.root5)

Is always square root with numbers less than 20 or something? I'm not good at maths so sorry for the dumb question!

I am good at maths so I can’t help you :biggrin:

Square numbers are numbers which times it selfs for ex ;
2x2 = 4
3x3= 9
4x4 16

So square root is the opposite. For example, of you are ask to find the square root of 25, you need to find the number that times itself to get 25. The answer? It’s 5 becuase 5 multiply by 5 is 25. To work this out, you need to divide the square root by prime number until you get 1.

So for example, if you want to find the square root of 81, you need to divide it by prime numbers.

81 ÷ 2 = no, you won’t get a whole number
81 ÷ 3 = 27. Now you need to divide 27 by prime numbers,
27÷2 = no
27÷3 = 9. Now you need to divide 9 by prime numbers
9÷2 = no
9÷3= 3. Divide 3 by prime numbers
3÷2= nope
3÷3 = 1. There we go! Finally got 1! Now you need to multiply the numbers which you divided the numbers with (in bold) and but it in

3x3x3x3 = ( is the same as 3²x3²⁾
To get the square root, we need to put the sure root in to 3²x3²

√ 3²x3²(remedy that square numbers cancel out square root. So √ 3²x3²becomes = 3x3. What is 3x3? 9! So the square root of 81 is 9

Reply 10

Maya memsaab

OP

14

Original post by Bathila

I am good at maths so I can’t help you :biggrin:

Square numbers are numbers which times it selfs for ex ;
2x2 = 4
3x3= 9
4x4 16

So square root is the opposite. For example, of you are ask to find the square root of 25, you need to find the number that times itself to get 25. The answer? It’s 5 becuase 5 multiply by 5 is 25. To work this out, you need to divide the square root by prime number until you get 1.

So for example, if you want to find the square root of 81, you need to divide it by prime numbers.

81 ÷ 2 = no, you won’t get a whole number
81 ÷ 3 = 27. Now you need to divide 27 by prime numbers,
27÷2 = no
27÷3 = 9. Now you need to divide 9 by prime numbers
9÷2 = no
9÷3= 3. Divide 3 by prime numbers
3÷2= nope
3÷3 = 1. There we go! Finally got 1! Now you need to multiply the numbers which you divided the numbers with (in bold) and but it in

3x3x3x3 = ( is the same as 3²x3²⁾
To get the square root, we need to put the sure root in to 3²x3²

√ 3²x3²(remedy that square numbers cancel out square root. So √ 3²x3²becomes = 3x3. What is 3x3? 9! So the square root of 81 is 9

This really helped! Thanks

Reply 11

Shibu the Doge

22

Original post by Mayavalentine

This really helped! Thanks

np! Happy to help. Tell me if you need anymore help. :smile:

Reply 12

Notnek

21

Original post by Mayavalentine

All help is appreciated

Just so you’re aware, in a GCSE exam you would not be asked to factorise this. Factorising at GCSE means that there are integers in the brackets so x^2-11 can’t be factorised at GCSE.

How do you factorise x^2-11

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you