Negitive Exponents Q: r^(-9) + r^(-8)

For the same reason that x + x = x[sup:1g6zf5xo]1[/sup:1g6zf5xo] + x[sup:1g6zf5xo]1[/sup:1g6zf5xo] is not equal to x[sup:1g6zf5xo]2[/sup:1g6zf5xo]. :wink:
 


Because r^(-8) is being ADDED to r^(-9), instead of being MULTIPLIED by r^(-9).

If the given expression were the following, instead, then we could simplify it as shown.

r^(-9) * r^(-8) = r^(-9 - 8) = r^(-17)

Will you please tell us the instructions that you received with this expression? (I don't know what you're supposed to do with it.)

There is no way to simplify the expression that you typed. Perhaps, you're supposed to rewrite it "without negative exponents". We can do that.

Are you familiar with the propery of exponents that allows us to rewrite a power with negative exponent?

For example:

r^(-5) = 1/r^5
 
there are no instructions just the problem but i think thats what they want me to do .... the answer is 1+r/r^5


i understand that property you just explained but i dont get how they got to that answer


if i did that property i would get to


1/r^9+1/r^8


and then.........
 
fresh83 said:
[There] are no instructions …
Click to expand...


There must be!

Any expression, in the absence of instructions, does not constitute a homework exercise.

Please, look again.

'
fresh83 said:
… the answer is 1+r/r^5 …
Click to expand...


Who told you this? Without instructions, there is no question to answer.

If the instructions are something like, "Rewrite the given sum as a single ratio containing no negative exponents", then this "answer" is wrong.

Without knowing what you're supposed to do with the given expression, I cannot help you.

You also need to be aware that when we type ratios that contain addition or subtraction, we need to use grouping symbols to be clear.

You typed 1 + r/r^5 . This means that you're adding 1 to the ratio r/r^5, so the expression simplifies to 1 + 1/r^4 .

I think you mean (1 + r)/r^5. In other words, the sum 1 + r is the numerator.

Point to the drop-down menu at the top of this page titled, "Forum Help", followed by clicking "Karl's Notes - Typing Math", to read about how to properly type mathematical expressions. 8-)

 
fresh83 said:
there are no instructions just the problem but i think thats what they want me to do .... the answer is 1+r/r^5
Click to expand...
NO; the answer is (1 + r) / r^9 ; YES, brackets NEEDED!
 
still confused

from the problem can i go:

r^(9)/1 +r^(8) ?


and if so ...what next ?
 
fresh83 said:
r^(9)/1 +r^(8) ?
Click to expand...


:roll:

Do you know how to add two fractions together? Please tell me, because, if you don't, then we need to back up quite a bit.

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

 
fresh83 said:
[No, I don't] think [that I] do …
Click to expand...


I'm thinking that you might not be ready to understand why the sum of 1/r^9 and 1/r^8 turns out to be (1+r)/r^9, even if I were to type out all of the steps.

Please CLICK HERE, and read over the five pages of lessons and examples for adding fractions. (These lessons start out using only numbers, and then they move on to adding algebraic ratios.)

After you become familiar with the steps involved (eg: finding a common denominator, expressing each ratio in terms of the common demoninator, combining the numerators), then try to do your exercise, again.

If you see anything at the PurpleMath site (or in your textbook examples, or your class notes, or anywhere else) that you do not understand, then ask specific questions right here, so that we might know what it is that you do not understand. We will help you learn by answering your specific questions.

If, after learning how to add two algebraic ratios, you would like more help with your exercise, then please show whatever work you can accomplish, and try to say something about WHY you're stuck, so that people might determine where to continue helping you.

Cheers 8-)

 
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