Math by armbar

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Solved it.

X=1/((1/A)+(1/B))

Too tired to think last night, I guess. I solved it by trying to think of some similar equation I might have done in the past. I don't have a clue about what it means. But, as said, I only have to know how to type it in my calculator.

phn by painful heel lock.:D
 
The engineer in you speaking, eh?

And here I was all happy having solved it on my own. Not bad, I think, considering I have forgot, if not everything, 95 pct of what I learned in high school. I think and hope this is HS level. But then, I probably have forgotten 95 pct of everything I learned in school. Thinking about it, I don't know what I learned in school other than being quite and feeling shame if you didn't. Man, what a hellhole it was.
 
If phn's calculator has a reciprocal function key (say "1/X" or x^-1); then the reciprocals of reciprocals is less keystrokes than the reciprocal of the LCD (least common denominator, A*B) form for 2 resistors even if A and B are only 1 digit each. You would enter: A, rec key, +, B, rec key, equal key, rec key

Also the reciprocal of the reciprocal form allows you to do a problem like: I need two resistors in parallel to make 10K and I have a 22K resistor, what do I need?

=> 1/((1/10K)-(1/22K)), without breaking a sweat!

The form A // B => A*B/(A+B), should never be taught; as it has no intuitive connection to conductance => 1/resistance which is at the heart of combining resistors in parallel and understanding how to calculate the answer in general.

Just an observation and opinion, all correct answers are equivalent!
VSR
 
frugal-phile™
Joined 2001
Paid Member
sherelec said:
If phn's calculator has a reciprocal function key (say "1/X" or x^-1); then the reciprocals of reciprocals is less keystrokes than the reciprocal of the LCD (least common denominator, A*B) form for 2 resistors even if A and B are only 1 digit each. You would enter: A, rec key, +, B, rec key, equal key, rec key

Even faster if you use a proper RPN calculator

A, 1/x, B. 1/x + 1/x

dave
 
sherelec said:
If phn's calculator has a reciprocal function key (say "1/X" or x^-1); then the reciprocals of reciprocals is less keystrokes than the reciprocal of the LCD (least common denominator, A*B) form for 2 resistors even if A and B are only 1 digit each. You would enter: A, rec key, +, B, rec key, equal key, rec key

Algebraic entry? Ugh! May as well use an abacus! Real men use RPN.

I_F
 
RPN and the Abacus

I knew when I entered the keystrokes into the reply that I would hear about RPN. I wish the stock market was as predictable!

I hesitated for 10s after putting the keystrokes in the reply. Then I remembered a trick I used for many years during design reviews; when I was obliged to submit several hundred pages of worst case analysis to support a board design in front of my boss and twenty of my "favorite" peers. On page one I made a glaring typo, and on page two I made an equally glaring analytical blunder. Thus, shielding myself from any further detailed examination for the remaining pages, and thus saving many wasted hours for all concerned.

My sister has lived in NYC all her adult live. She told me once that during NYC's infamous blackouts the only establishments that seem to be in business are those that are abacus enabled.

The reason the keystrokes were in algebraic notation is because I purchased an inexpensive algebraic scientific calculator in 1985. It is solar powered, steel and plastic, fits my pocket and it will not die. It has outlived all my calculators purchased before and since. As my fingers stiffen and I loose my manual dexterity, I have no one to blame but myself and my algebraic calculator for accelerating my deterioration from having to enter all those extra keystrokes for over 20 years!

Best wishes,
VSR
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.