This is discrete functions. Can someone please help?? I can't figure out what I am doing wrong. I am supposed to get the indicated sum, but I keep doing something wrong. This is what series I have to work with x[15] for 0.3+0.003+0.00003+...... I know that a=0.3 and r=0.01 and n=15. so x[n] = a(r^n-1)/r-1
x[n] = 0.3((0.01)^15-1)/0.3-1
x[n] = 0.3((-1))/-7/10
but the outcome is 3/7. Is that the right outcome because the back of my text book says it's 10/33. And I don't understand what I am doing wrong. :/

Question

This is discrete functions. Can  someone please help?? I can't figure out what I am doing wrong. I am supposed to get the indicated sum, but I keep doing something wrong. This is what series I have to work with x[15] for 0.3+0.003+0.00003+...... I know that a=0.3 and r=0.01 and n=15. so x[n] = a(r^n-1)/r-1
x[n] = 0.3((0.01)^15-1)/0.3-1
x[n] = 0.3((-1))/-7/10
 but the outcome is 3/7. Is that the right outcome because the back of my text book says it's 10/33. And I don't understand what I am doing wrong. :/

klimenkov · Answer

What is $0.01^{15}$?

anonymous · Answer

that would be the common ratio or "r" to the exponent number of terms or "n"

klimenkov · Answer

Can you calculate this?

anonymous · Answer

Yes, when I calculate it I get 1.E-30, then I subtract 1 and get -1

klimenkov · Answer

There is a mistake in the denominator.
x[n] = 0.3((0.01)^15-1)/0.3-1

anonymous · Answer

oh

anonymous · Answer

wow, I am so clueless

klimenkov · Answer

Actually, there are two mistakes.

anonymous · Answer

Okay I see where I went wrong. Wow

anonymous · Answer

Thank you so much :)