# this might be simple... but i dont know

• Sep 11th 2006, 05:07 PM
eah1010
this might be simple... but i dont know
ok help.. this might sound super easy... but i cant seem to get it... i thought the answer was 1 but my teacher said it was wrong...

2^29 - 2^28
__________
2
• Sep 11th 2006, 05:13 PM
Quick
Quote:

Originally Posted by eah1010
ok help.. this might sound super easy... but i cant seem to get it... i thought the answer was 1 but my teacher said it was wrong...

2^29 - 2^28
__________
2

A big thing to watch out for is the fact that x^a-x^b does not equal x^(a-b)

Now you have problem: (2^29-2^28)/2

distribute: (2^29)/(2)-(2^28)/(2)

divide: 2^28-2^27

factor: (2^27)(2-1)

subtract: (2^27)(1)

• Sep 11th 2006, 05:16 PM
Jameson
Well try testing smaller numbers to see why you can't just subtract.

Let's try 2^3-2^2. Expanding out both terms gives you 8-4=4. Now let's factor this to see if that can make some sense. 2^3-2^2=2^2(2-1)=2(1)=2

Apply this same technique to your problem.

2^29-2^28=2^28(2-1)=2^28(1)=2^28

And divide by two. So (2^28)/2=2^27
• Sep 11th 2006, 05:22 PM
eah1010
thank you so much! you guys rock!