Yahoo Answers is shutting down on May 4th, 2021 (Eastern Time) and beginning April 20th, 2021 (Eastern Time) the Yahoo Answers website will be in read-only mode. There will be no changes to other Yahoo properties or services, or your Yahoo account. You can find more information about the Yahoo Answers shutdown and how to download your data on this help page.
Trending News
simplify: 7^(-20) - 7^(-21)?
please tell me a way to do this sum..........use rules of indices if possible
7 Answers
- RogueLv 78 years ago
7^-20 - 7^21
given a^-n = 1/a^n
=> 1/7^20 - 1/7^21
=> (1/7^20 *7/7^1) - 1/7^21
given a^n * a^m = a^(n m)
=> 7/7^21 - 1/7^21
=> 6/7^21
=> 6/558545864083284007
Source(s): http://mathematicsi.com/rules-of-indices/ - kritty karnaLv 58 years ago
7^(-20) - 7^(-21)
= 1/ {7^20} - 1/(7^21)
=(1* 7^21) - 1} / 7^21
=(7^21 -1) / 7^21
= {7^21 - (7^0)} /7^21 [a^0 =1,then 7^0=1 ]
= {7^(21-0)} / 7^21
= 7^21 /7^21
=1
- How do you think about the answers? You can sign in to vote the answer.
- Anonymous7 years ago
We invite you to join the Armis team
- 8 years ago
7 ⁻²⁰ â 7 ⁻²¹
=7⁻²⁰(1 â 7 ⁻¹ )
=7⁻²⁰(1 â 1/7)
=7⁻²⁰(6/7)
=6Ã7⁻²¹(Ans)
