The Student Room Group

C1 Graph transformations of 1/x graphs

Here is a graph of y=3xy=\dfrac {3}{x}
https://www.google.co.uk/search?q=graph+of+y%3D3/x&biw=1920&bih=955&source=lnms&sa=X&ved=0ahUKEwjg9LaBwffLAhWC5RoKHRfTDh4Q_AUIBigA&dpr=1

Find the Co-ordinates where y=3x+2y=\dfrac{3}{x+2} touches any of the co-ordinate axis. x2x \not = -2

how would i know the graph moves to the left using the y=f(x+2) rule which moves the graph to the left by 2 units?
(edited 8 years ago)
Reply 1
Original post by thefatone
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You have the f(x)=3xf(x) = \frac{3}{x}. Then f(x+2)=3x+2f(x+2) = \frac{3}{x+2} shifts the graph two units to the left, so there will be one intersection with the y-axis.

This is given when f(0+2)=30+2=f(2)=f(0+2) = \frac{3}{0 + 2} = f(2) = \cdots. The shift is horizontal and hence there is still no x-axis intersections.
Reply 2
Original post by Zacken
You have the f(x)=3xf(x) = \frac{3}{x}. Then f(x+2)=3x+2f(x+2) = \frac{3}{x+2} shifts the graph two units to the left, so there will be one intersection with the y-axis.

This is given when f(0+2)=30+2=f(2)=f(0+2) = \frac{3}{0 + 2} = f(2) = \cdots. The shift is horizontal and hence there is still no x-axis intersections.


so it doesn't matter where the x is in this one? so if this function has a 2x then i half the x -value for example?
Reply 3
Original post by thefatone
so it doesn't matter where the x is in this one? so if this function has a 2x then i half the x -value for example?


I don't understand what you're saying.
Reply 4
Original post by Zacken
I don't understand what you're saying.


so if the function instead ofy=3x+2y=\dfrac{3}{x+2} was y=32x y=\dfrac{3}{2x} would the x-values be halved? i don't think this function y=32x y=\dfrac{3}{2x} would touch any axis right?
Reply 5
Original post by thefatone
so if the function instead ofy=3x+2y=\dfrac{3}{x+2} was y=32x y=\dfrac{3}{2x} would the x-values be halved? i don't think this function y=32x y=\dfrac{3}{2x} would touch any axis right?


It would represent and horizontal stretch scale factor 12\frac{1}{2} or a vertical stetch scale factor 12\frac{1}{2} (the vertical/horizontal thingies being the same is due to the fact that 1/x is its own inverse function. Cool, right? Anyways, doesn't matter). There still wouldn't be any axis intersections, yes. It is not a shift, just a stretch.
Reply 6
Original post by Zacken
It would represent and horizontal stretch scale factor 12\frac{1}{2} or a vertical stetch scale factor 12\frac{1}{2} (the vertical/horizontal thingies being the same is due to the fact that 1/x is its own inverse function. Cool, right? Anyways, doesn't matter). There still wouldn't be any axis intersections, yes. It is not a shift, just a stretch.


ah right i see thanks for that ^-^
Reply 7
Original post by thefatone
ah right i see thanks for that ^-^


You're welcome.

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