D desiderius1 Apr 2010 43 1 May 10, 2010 #1 \(\displaystyle \sum_{k=1}^6(-1)^k4^k \) The answer is: 3276 How do you do this problem? \(\displaystyle -1^6=1\) \(\displaystyle 4^6=4096\) 4096 != 3276 Thanks.

\(\displaystyle \sum_{k=1}^6(-1)^k4^k \) The answer is: 3276 How do you do this problem? \(\displaystyle -1^6=1\) \(\displaystyle 4^6=4096\) 4096 != 3276 Thanks.

S sa-ri-ga-ma Jun 2009 806 275 May 10, 2010 #2 desiderius1 said: \(\displaystyle \sum_{k=1}^6(-1)^k4^k \) The answer is: 3276 How do you do this problem? \(\displaystyle -1^6=1\) \(\displaystyle 4^6=4096\) 4096 != 3276 Thanks. Click to expand... It is a GP with first term -4, common ratio r = -4 and number of terms 6. So sum S = a[r^n - 1]/(r-1) = -4(4096 - 1)/(-4-1) Now find the answer.

desiderius1 said: \(\displaystyle \sum_{k=1}^6(-1)^k4^k \) The answer is: 3276 How do you do this problem? \(\displaystyle -1^6=1\) \(\displaystyle 4^6=4096\) 4096 != 3276 Thanks. Click to expand... It is a GP with first term -4, common ratio r = -4 and number of terms 6. So sum S = a[r^n - 1]/(r-1) = -4(4096 - 1)/(-4-1) Now find the answer.