Function: Find a point on a graph by shifting  TOPIC_SOLVED

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Function: Find a point on a graph by shifting

Postby Alan51q on Mon Apr 28, 2014 11:35 pm

Problem:

Suppose (-3,5) is a point on the graph of y=g(x),
What point is on the graph of y=g(3x+9)?

The book gives the answer as (-4,5), I'm assuming, by first subtracting 9 from -3 and then multiplying -12 by 1/3 to get the x coordinate. However, given the standard order of operations, I can't figure out why it shouldn't be (-10,5) by first multiplying 1/3 by -3 to get -1 and then subtracting -9 to get the x coordinate.

If anyone can help me understand why, I'd be thankful.
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Re: Function: Find a point on a graph by shifting  TOPIC_SOLVED

Postby FWT on Tue Apr 29, 2014 12:16 pm

Alan51q wrote:Suppose (-3,5) is a point on the graph of y=g(x),
What point is on the graph of y=g(3x+9)?

The book gives the answer as (-4,5), I'm assuming, by first subtracting 9 from -3 and then multiplying -12 by 1/3 to get the x coordinate. However, given the standard order of operations, I can't figure out why it shouldn't be (-10,5) by first multiplying 1/3 by -3 to get -1 and then subtracting -9 to get the x coordinate.

They give some info on this here. I think you do it like this:

x = -3 is on the graph
3x+9 HAS TO equal -3 to be on the graph (because that's the ONLY x we KNOW is ok)
3x+9=-3
3x=-12
x=-4

Then plug in & get y=5 (because that's the y they gave us).
FWT
 
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Re: Function: Find a point on a graph by shifting

Postby Alan51q on Tue Apr 29, 2014 4:57 pm

FWT wrote:
Alan51q wrote:Suppose (-3,5) is a point on the graph of y=g(x),
What point is on the graph of y=g(3x+9)?

The book gives the answer as (-4,5), I'm assuming, by first subtracting 9 from -3 and then multiplying -12 by 1/3 to get the x coordinate. However, given the standard order of operations, I can't figure out why it shouldn't be (-10,5) by first multiplying 1/3 by -3 to get -1 and then subtracting -9 to get the x coordinate.

I think you do it like this:

x = -3 is on the graph
3x+9 HAS TO equal -3 to be on the graph (because that's the ONLY x we KNOW is ok)
3x+9=-3
3x=-12
x=-4

Then plug in & get y=5 (because that's the y they gave us).


Thanks for this. It makes total sense to solve it that way. I don't know why it wouldn't be explained that way in the book.
Alan51q
 
Posts: 5
Joined: Fri Feb 21, 2014 9:47 pm


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