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# How to solve 2x^2+11=x+21 watch

1. How to solve 2x^2+11=x+21
2. Put all of the equation onto one side.

Then factorise.

The brackets will be (2x +/- a)(x +/- b) because they are the only factors of 2x^2

Can you do it from there?
3. I got (2x-5)(x+2)

but then i don't know what to do from there on to find what "X" is. I know this is a easy question but my teacher is really bad at teaching
4. (Original post by RoyTheToy)
I got (2x-5)(x+2)

but then i don't know what to do from there on to find what "X" is. I know this is a easy question but my teacher is really bad at teaching
Ok the original equation was 2x^2 - x - 10 = 0

This means that (2x-5)(X+2) will equal 0 as well

For this to happen if either bracket is equal to zero the equation will be zero overall.

Therefore 2x-5 = 0 or x + 2 = 0

2x= 5 or x = -2

x = 5/2 or x = -2
5. great, thanks very much for explaining to me

i really appreciate it

thank you so much
6. no no no, no factorise!!!!!!........

Divide both sides by X: X = 2X+11 = 21

Take 11 from both sides: 2X = 10

Dive both sides by 2: X=5
7. (Original post by J17)
no no no, no factorise!!!!!!........

Divide both sides by X: X = 2X+11 = 21

Take 11 from both sides: 2X = 10

Dive both sides by 2: X=5
I'm not quite sure what you've done there
8. (Original post by J17)
no no no, no factorise!!!!!!........

Divide both sides by X: X = 2X+11 = 21

Take 11 from both sides: 2X = 10

Dive both sides by 2: X=5

that is a way to find one of the solutions, but as there is a squared number in there (which its self has two solutions) you would then have to find the other solution.

(remember the square root of a number has two answers)

if you wished you could also plug it into the quadratic formula or complete the square, but with something that simple it is easiest to factorise.
9. (Original post by J17)
no no no, no factorise!!!!!!........

Divide both sides by X: X = 2X+11 = 21

Take 11 from both sides: 2X = 10

Dive both sides by 2: X=5
this is what i did
yea people say factorise but it's much easier than that
10. OK. Will the residents of this thread please observe that the "divide" technique gives the wrong number of solutions, AND 5 doesn't even satisfy the equation!
11. (Original post by J17)
no no no, no factorise!!!!!!........

Divide both sides by X: X = 2X+11 = 21

Take 11 from both sides: 2X = 10

Dive both sides by 2: X=5
This method is wrong.

2x^2 + 11 = x + 21
2x + 11 = 21

That is not how you divide both sides by x.

x = 5 is not the correct answer.
12. how you solve?? 2x^2+11=x+21
first you minus 21 from both sides...so you get 2x^2-10=x
and then you minus x to both sides
so you get 2x^2-x-10=0
then you factorise you put them into brackets ...
(2x-5)(x+2) = 0
so if y=0 then..... x= -2 or x= 5/2
when x=0 then.... y= -10

hope that helps
13. since when is (x+21)/x = 21???
its 1+21/x people!!
factorisation/quadratic equation/completing the square/graph are the only way to solve quadratic equations!
14. and inspection
15. (Original post by J17)
no no no, no factorise!!!!!!........

Divide both sides by X: X = 2X+11 = 21

Take 11 from both sides: 2X = 10

Dive both sides by 2: X=5
you loose a solution if you do that.....
16. if you divide both sides by X then you have to divide every term by x which will leave you with 11/x and 21/x surely?
17. (Original post by J17)
STFU NERD, congrats on the uni offers, need more than grades for top unis
exactly what makes me wonder how you got in. they must've been blind-folded.

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