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Math grade 12 helpp

Can someone explain how to do 4c1632057016990.jpg
(edited 2 years ago)
Reply 1
You have two equations for R1 and R2, so write them down and solve them simultaneously.
Post your progress if you get stuck.
They gave us that these resistors are in parallel, and hence the Total resistance, T, will have the formula of 1/T = 1/R1 + 1/R2. We know that R1=R1 and we know that R2 = R1 + 3. So subbing this in to the formula that they gave us:
1/T = 1/R1 + 1/(R1+3)
Through simplification we can rearrange to get T= (R1^2 + 3R1)/2R1+3. Now sub in R1 = 1 + 1/8 in the equation to find T
(edited 2 years ago)
Reply 3
Original post by chinjyanson
They gave us that these resistors are in parallel, and hence the ...

A bit like your other post, can you edit/delete and just provide hints and let the OP do as much of the work as possible?
The guidelines are described in the sticky at the top of the forum.
https://www.thestudentroom.co.uk/showthread.php?t=4919248
(edited 2 years ago)
Reply 4
Original post by mqb2766
You have two equations for R1 and R2, so write them down and solve them simultaneously.
Post your progress if you get stuck.

1632210755990.jpgthis is what I got so far
Reply 5
Original post by chinjyanson
They gave us that these resistors are in parallel, and hence the Total resistance, T, will have the formula of 1/T = 1/R1 + 1/R2. We know that R1=R1 and we know that R2 = R1 + 3. So subbing this in to the formula that they gave us:
1/T = 1/R1 + 1/(R1+3)
Through simplification we can rearrange to get T= (R1^2 + 3R1)/2R1+3. Now sub in R1 = 1 + 1/8 in the equation to find T

Shouldn't it be x3 not +3?
Reply 6
Main mistake is when you add (combine) two fractions. If the two resistors are A and B
1/A + 1/B = ...
Simply add the fractions as normal. I'd do the substition about one resistor being 3 greater (+3), when you've got the basic algebra done.

Its also easier to write 1 1/8 in improper form.
(edited 2 years ago)
Reply 7
Original post by chinjyanson
They gave us that these resistors are in parallel, and hence the Total resistance, T, will have the formula of 1/T = 1/R1 + 1/R2. We know that R1=R1 and we know that R2 = R1 + 3. So subbing this in to the formula that they gave us:
1/T = 1/R1 + 1/(R1+3)
Through simplification we can rearrange to get T= (R1^2 + 3R1)/2R1+3. Now sub in R1 = 1 + 1/8 in the equation to find T

1632211096313.jpg so according to u I should do what's on the right side
But I don't get how u got last equation
Reply 8
One resisitor is +3 Ohms larger than the other one, not 3 times larger. Also it does not look like you're adding fractions correctly.

You seem to have copied the last expression on the page from the earllier post, but your working is incorrect to get there.
[br]R2=R1+3[br][br]R_2 = R_1 + 3[br]
(edited 2 years ago)
Reply 9
Original post by mqb2766
One resisitor is +3 Ohms larger than the other one, not 3 times larger. Also it does not look like you're adding fractions correctly.

You seem to have copied the last expression on the page from the earllier post, but your working is incorrect to get there.
[br]R2=R1+3[br][br]R_2 = R_1 + 3[br]

I see
Appreciate the help
Original post by mqb2766
Not a good idea give your details on line.

Its just an email address
Original post by Ava_Watson
Its just an email address

Sure, its a new user whos spamming several forums and is likely to be banned shortly.
Your shout though.

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