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Stuck on C1 equation

Hi, I am doing C1 further equations and seem to be getting all the others including ones which are similar to this equation but cannot seem to get this one

Here is the equation:


2x = (45 over x) -1

Thanks for help

The answer in the book is 9 over 2 or -5

I keep getting the answer postive/negative root 22

Any help on the method would be great

Thanks :smile:
See what happens if you multiply the equation by x.
Reply 2
Avatar for mccrae01
mccrae01
18
Doing it in my head I also get that root 22. Maybe the book is wrong?
Original post by felamaslen
See what happens if you multiply the equation by x.


I have done this and get:

2x squared = 44

x squared = 22

so x = +/- root 22

which is wrong
Original post by mccrae01
Doing it in my head I also get that root 22. Maybe the book is wrong?


I am very confused too, the book is cambridge Core 1 for AQA?
Okay, you have:

2x=45x−12x=\frac{45}{x} - 1

How can you remove the fraction - in other words, take x to the other side?


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I got the answer in the book. Remember to multiply every term by x. :smile:


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Original post by kingaaran
Okay, you have:

2x=45x−12x=\frac{45}{x} - 1

How can you remove the fraction - in other words, take x to the other side?


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Multiply by x


I have tried another method and have:

2x squared + x = 45
(edited 10 years ago)
Original post by Peace&Love
I have done this and get:

2x squared = 44

x squared = 22

so x = +/- root 22

which is wrong


You're not multiplying the -1 term by x.
Original post by Peace&Love
Multiply by x


I have tried another method and have:

2x squared + x = 45


Yeah, I think that when you were multiplying through by xx, you were perhaps forgetting to multiply the −1-1 term by xx.

With that method, you're on the right path. What type of equation is that and how do you solve it? :biggrin:


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Original post by felamaslen
You're not multiplying the -1 term by x.



If i do i get:

2x squared + x = 45

how do i simplfy this?.
Original post by kingaaran
Yeah, I think that when you were multiplying through by xx, you were perhaps forgetting to multiply the −1-1 term by xx.

With that method, you're on the right path. What type of equation is that and how do you solve it? :biggrin:


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Do i have to make it a quadratic? then factorise/complete the square/ use quadratic formula?
Original post by Peace&Love
Do i have to make it a quadratic? then factorise/complete the square/ use quadratic formula?


It is a quadratic equation :biggrin:

To solve a quadratic equation, you have to make it equal to zero, and then use one of the above methods, depending on the quadratic. What do you get if you do that? :wink:


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Original post by kingaaran
It is a quadratic equation :biggrin:

To solve a quadratic equation, you have to make it equal to zero, and then use one of the above methods, depending on the quadratic. What do you get if you do that? :wink:


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sorry thats what i meant do I have to make it equal zero

I have (-1 +/- squared root of 361) over 4?
Original post by Peace&Love
sorry thats what i meant do I have to make it equal zero

I have (-1 +/- squared root of 361) over 4?


Well the square root of 361 is 19 IIRC, so that makes 9/2 or -5 as quoted in the OP.
(edited 10 years ago)
2x2+x−45=(2x−9)(x+5)2x^2 + x - 45 = (2x - 9)(x + 5)
Original post by Peace&Love
sorry thats what i meant do I have to make it equal zero

I have (-1 +/- squared root of 361) over 4?


That's correct:

x=−1±3614 x=\frac{-1\pm \sqrt{361}}{4}, which you will find will give you with the answers from the textbook. I hope I helped. If you need anymore help, just ask. :biggrin:


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