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ALevel Maths Fiding roots of the equation. Please help (EASY)

Hi, i'm just revising some AS maths and I have (stupidly) forgot how to answer this question...

Curve has equation f(x)=8/x+1/2x-5
(i) find roots of equation 2f(x) =0
for this I doubled the 8/x+1/2x-5 to get 16/x+x+10 and made equal 0. I got the answer x=8 or x=2. is this right???

(ii) find roots of equation f(4x)=0.
i'm not sure how to approach this question. what do I need to do??
Reply 1
Original post by aliasanoynmous
Hi, i'm just revising some AS maths and I have (stupidly) forgot how to answer this question...

Curve has equation f(x)=8/x+1/2x-5
(i) find roots of equation 2f(x) =0
for this I doubled the 8/x+1/2x-5 to get 16/x+x+10 and made equal 0. I got the answer x=8 or x=2. is this right???

(ii) find roots of equation f(4x)=0.
i'm not sure how to approach this question. what do I need to do??

Your equations are unreadable so please edit your post to include brackets. For example, 8/x+1/2x-5 could mean (8/x) + 1/(2x) - 5 or it could mean 8/x + 1/(2x-5) etc.
Original post by Notnek
Your equations are unreadable so please edit your post to include brackets. For example, 8/x+1/2x-5 could mean (8/x) + 1/(2x) - 5 or it could mean 8/x + 1/(2x-5) etc.


Apologies, these are the equations rewritten.
equations.JPG
Reply 3
Original post by aliasanoynmous
Hi, i'm just revising some AS maths and I have (stupidly) forgot how to answer this question...

Curve has equation f(x)=8/x+1/2x-5
(i) find roots of equation 2f(x) =0
for this I doubled the 8/x+1/2x-5 to get 16/x+x+10 and made equal 0. I got the answer x=8 or x=2. is this right???

(ii) find roots of equation f(4x)=0.
i'm not sure how to approach this question. what do I need to do??

For (i) your answer is correct.

For (ii), do you know what f(4x) is?
Original post by Notnek
For (i) your answer is correct.

For (ii), do you know what f(4x) is?


I understand it in the context of graph transformations. So, that means divide the x coordinates by 4. But not in the context of this question.
Original post by aliasanoynmous
Hi, i'm just revising some AS maths and I have (stupidly) forgot how to answer this question...

Curve has equation f(x)=8/x+1/2x-5
(i) find roots of equation 2f(x) =0
for this I doubled the 8/x+1/2x-5 to get 16/x+x+10 and made equal 0. I got the answer x=8 or x=2. is this right???

(ii) find roots of equation f(4x)=0.
i'm not sure how to approach this question. what do I need to do??


Take the original function. Wherever it says x, replace it with 4x. So for example, the term 8/x becomes 8/4x which is equal to 2/x.
Original post by TheMindGarage
Take the original function. Wherever it says x, replace it with 4x. So for example, the term 8/x becomes 8/4x which is equal to 2/x.

Thank you so much. Fingers crossed this is correct!Capture2.JPG
Reply 7
Original post by aliasanoynmous
Thank you so much. Fingers crossed this is correct!Capture2.JPG


Yes, those solutions are correct. :smile:

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