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Having real problems getting my head around this one too:

 

Make x the subject

 

y = 1/x.           Answer x = 1/y

 

I have been told to cross multiply, I get the theory of this but how can I cross multiply with the y when it is not a fraction?

 

Thanks

Walthamx  Jan 29, 2018

Best Answer 

 #1
avatar+92917 
+2

I suggest you study the other one. 

also, I know a lot of teachers talk about cross multiply but iI think it is a confusing way to teach it.

It is easy I guess but the logic is not very obvious.

 

What you must ALWAYS do is the SAME thing to each side. The equation must always balance!

 

the pic is showing that if you add 10 to one side then you must add 10 to the other side too,

otherwise the scale would become unbalanced!

 

 

Now ot your p[roblem:

 

\(y = \frac{1}{x}\\ \text{First make both sides a fraction}\\ \frac{y}{1} = \frac{1}{x}\\ \text{Now you want x on the top so turn BOTH sides upside down (take the reciprocals)}\\ \frac{1}{y}= \frac{x}{1}\\ \frac{1}{y}= x\\ \text{Now swap sides}\\ x=\frac{1}{y}\)

Melody  Jan 29, 2018
 #1
avatar+92917 
+2
Best Answer

I suggest you study the other one. 

also, I know a lot of teachers talk about cross multiply but iI think it is a confusing way to teach it.

It is easy I guess but the logic is not very obvious.

 

What you must ALWAYS do is the SAME thing to each side. The equation must always balance!

 

the pic is showing that if you add 10 to one side then you must add 10 to the other side too,

otherwise the scale would become unbalanced!

 

 

Now ot your p[roblem:

 

\(y = \frac{1}{x}\\ \text{First make both sides a fraction}\\ \frac{y}{1} = \frac{1}{x}\\ \text{Now you want x on the top so turn BOTH sides upside down (take the reciprocals)}\\ \frac{1}{y}= \frac{x}{1}\\ \frac{1}{y}= x\\ \text{Now swap sides}\\ x=\frac{1}{y}\)

Melody  Jan 29, 2018

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