jacko
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 posted on 21/1/05 at 04:48 PM |
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maths genius? We need help
Help we have been trying to help our daughter with her homework. Question Create a graph from each of the following functions. Use the starting points
given with each function to find co-ordinates.
We are stuck on one of the questions.
y = 4x -3
{1,2,3,4}
We know how to calculate them but are not sure how to put them on the graph ie which way do they go.
when calculating the numbers the answer does not have a minus in front of it does this mean you go diagonaly upwards or do you treat the coordinates
as minus and go downwards from zero. Any help will be appreciated as we are stuck and she doesnt want to go back to the teacher on Monday and get told
off for not listening properly. Graham [Jacko
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GazzaP
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| posted on 21/1/05 at 04:59 PM |
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if it helps y is up and x is across.
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mattpilmoor
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| posted on 21/1/05 at 05:01 PM |
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Hi
Have a look at the graph in my picture archive (called graph for jacko). I'd have added it to the post but i'm not sure how to get
pictures in!
Hope it helps
Matt
Measure twice - Cut once - Still f*!K it up!
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wheelsinsteadofhooves
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| posted on 21/1/05 at 05:09 PM |
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aggghh, just wrote full explanation but not logged in so lost,
anyway, here we go again.
as mentioned the "y" refers to the vertical (up) axis and the x to the horizontal axis. positive is going up for y and to the right for x.
the gradient of a line is the change in y divided by the change in x, a positive gradient going from bottom left to top right.
to get the curve plot the numbers given (presume for x) against the correspnding value for y (or the other way round)
ie
x = 1, y = 4 x 1 - 3 = 1
x = 2, y = 5
thebn get the gradient by the above method
trick: all straight lines have an equation in the form of y = mx + c, where m is the gradient and c is the intercept with the y axis. therefore your
daughters graph should cross the y axis at -3 and have a gradient of 4 (sloped as described above).
hope this helps,
zane
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mattpilmoor
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| posted on 21/1/05 at 05:40 PM |
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A note about my previous post - In that picture the x-axis begins at 1 which is bad practice and should start at zero. Hence check out 'Graph 2
for Jacko' in my archive. Should get full marks!
Matt
Measure twice - Cut once - Still f*!K it up!
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flak monkey
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| posted on 21/1/05 at 05:57 PM |
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Sometimes i wish i could go back to maths like that...
Beats second order differental equations any day....
Sera
http://www.motosera.com
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jacko
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| posted on 21/1/05 at 06:13 PM |
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Many thanks to everyone who replied to
my daughters dilemma. Excellent graph Matt and excellent explanation Zane we have printed off the answers so she can keep it in her school bag.
from Graham and Amanda the daughter. Back next week with the next maths problem no doubt.........
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Liam
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| posted on 21/1/05 at 06:59 PM |
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quote:
Originally posted by mattpilmoor
A note about my previous post - In that picture the x-axis begins at 1 which is bad practice and should start at zero. Hence check out 'Graph 2
for Jacko' in my archive. Should get full marks!
Matt
Oooh, I dont know about that y-axis starting at -5 either!! I always thought the origin ought to be at (0,0). Er, loose one mark!
Liam
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JoelP
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| posted on 21/1/05 at 07:06 PM |
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make it a 4 segment graph, showing -20 to +20 on the y-axis, and -5 to +5 on the x-axis, centred on 0,0. Then it really will go down well!
Beware! Bourettes is binfectious.
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ceebmoj
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| posted on 21/1/05 at 08:45 PM |
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quote:
Originally posted by flak monkey
Sometimes i wish i could go back to maths like that...
Beats second order differental equations any day....
wish I could go back to maths like that as oposed to the freakky styff we do now.
(invers kinimatics for 2 10degrees of fredome rmes at the moment)
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krlthms
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| posted on 23/1/05 at 03:38 AM |
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quote:
Originally posted by Liam
quote:
Originally posted by mattpilmoor
A note about my previous post - In that picture the x-axis begins at 1 which is bad practice and should start at zero. Hence check out 'Graph 2
for Jacko' in my archive. Should get full marks!
Matt
Oooh, I dont know about that y-axis starting at -5 either!! I always thought the origin ought to be at (0,0). Er, loose one mark!
Liam
Origin does not have to start at 0,0; it dedpends on context. E.g, stock market numbers do not start at 0,0 axis. In general, your axes should be
slightly bigger than your data set. By "bigger" I , mean one tick. So, if your x axis dataset is 1 to 4, in increments of 1, then an x
axis of 0, to 5 would be sufficient. For Y axis, I would start at -2, and increment by 2 to +10.
Cheers
KT
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JoelP
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| posted on 23/1/05 at 08:54 AM |
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technically graphs are meant to start at 0,0, its just people are slack, hence graphs in media (news or advertising)often just start where they want.
But i think in school stuff it would be bad practice not to start at 0,0.
Beware! Bourettes is binfectious.
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MikeRJ
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| posted on 23/1/05 at 05:22 PM |
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quote:
Originally posted by JoelP
technically graphs are meant to start at 0,0, its just people are slack, hence graphs in media (news or advertising)often just start where they want.
But i think in school stuff it would be bad practice not to start at 0,0.
Generaly the graphs published showing statistics have their axis scaling and start points deliberately mangled to make the figures look better (or
worse) than they really are.
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