Hi, I'm stuck. I am trying to create a formula that will set a variable inversely to another variable, but to a varying proportion. To clarify, I need variable b to be set as follows: a=85, b=78; a=95, b=75. As you see, the y=k/x doesn't work because k is not the same for the two examples. Any help here will be greatly appreciated.
Need help with inverse formula
- Thread starter mad_miss
- Start date
D
Deleted member 4993
Guest
There are various methods of achieving that?
First of all - how do you know that - 'a' is NOT proportional to '1/b2'? or '1/b3'?
Please post the EXACT assignment that you are trying to solve (a photo will be good).
Please show us what you have tried and exactly where you are stuck.
Please follow the rules of posting in this forum, as enunciated at:
READ BEFORE POSTING
Please share your work/thoughts about this problem.
Dr.Peterson
Elite Member
- Joined
- Nov 12, 2017
- Messages
- 16,092
If this is not for an assignment, you'll have to state the problem fully and clearly. "Set a variable inversely to another variable, but to a varying proportion" is not at all clear! Please explain the circumstances and the goal as specifically as possible. Presumably you know more than just the two pairs of values you show.
HallsofIvy
Elite Member
- Joined
- Jan 27, 2012
- Messages
- 7,763
Perhaps you simply mean that "as a increases b decreases". That is, that the derivative is negative. One method is to set b= ua+ v with a negative. Here when a= 85, b= 78 so 78= 85a+ v. And when a= 95, b= 75 so 75= 95a+ b. Subtracting the first equation from the second, 3= 10a so a= 3/10. then 76= 95(3/10)+ b= 28.5+ b so b= 76- 28.5= 47.5.
Ok, sorry for not being more clear. The thing I was trying to accomplish was to reset the cooling setpoint on my thermostat based on outside temperature. When the weather gets hotter I want the cooling set lower and vice versa.
I figured out how to do it using y=mx+b. The controller I'm using can only process basic math so I did it in individual simple equations (m*outside temp stored in a variable, then that variable+b stored in the setpoint variable). So if the outside temp is between 85 & 95, the setpoint ranges from 78 to 75. If outside air goes out of that range it just stays at the high or low it was last set to.
I figured out how to do it using y=mx+b. The controller I'm using can only process basic math so I did it in individual simple equations (m*outside temp stored in a variable, then that variable+b stored in the setpoint variable). So if the outside temp is between 85 & 95, the setpoint ranges from 78 to 75. If outside air goes out of that range it just stays at the high or low it was last set to.