Graph identification

[Mtrader]

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I am having a bit of trouble identifying graphs. It takes me a long time to recognize if a relationship is liner or nonlinear.

I always know if the relationship is inverse or not but picking the a curved graph or straight graph either takes a long time (actually rearranging the formula) or is just a best guess. Any advice on how to identify them quicker?

 

[circulus vitios]

Can you give us some examples?

 

[Mtrader]

Sure, an easy example is EK1001 gchem question 162.

ideal gas shows what realsionship with preassure and volume?
the answers are all graphs

easy enough. They are inversly proportional so sloping downward but straight line down or curved sloping down?

This one is pretty easy but some of the more difficult questions say from a unfamiliar equations give me problems.

im not sure if i approach theses correctly since it seems to take me too long. i have to rearange the equations. is there a better way?

 

[circulus vitios]

Temperature is constant so solve for T and get T=PV/nR=Constant.

Look at the graphs and you see that pressure is plotted against volume, so we need to play with those variables.

Let's increase P by some arbitrary amount, let's say 5. The ratio then gets larger: (5P)V/nR=Constant. Remember that the right side of the equation needs to remain constant, so the ratio needs to remain constant. We need to cancel out P's increase of 5 by dividing V by 5: (5P)(V/5)=nR=Constant.

In summary, whenever we increase P we decrease V. Look at the graphs.

A. P increases as V decreases.
B. P increases as V increases.
C. P increases as V decreases.
D. P Increases as V increases.

So it's either A or C and it's now a question of: do we have an inverse relationship or a multiplicative inverse relationship? (If you don't remember, the inverse looks like y=a-bx for some constants a & b; the multiplicative inverse looks like y=1/x.)

We used multiplication/division to maintain our constant ratio. We therefore want a graph that looks like y=1/x, or graph C.

 

[Mtrader]

So it's either A or C and it's now a question of: do we have an inverse relationship or a multiplicative inverse relationship? (If you don't remember, the inverse looks like y=a-bx for some constants a & b; the multiplicative inverse looks like y=1/x.)

We used multiplication/division to maintain our constant ratio. We therefore want a graph that looks like y=1/x, or graph C.

wow thanks! this is the part that ive been missing. i should have been paying more attention in 9th grade! thanks again this is exactly what i was looking for.