+129849 7. Sum of a geometric series =
First term * [ 1 - common ratio^ (number of terms) ] / [ 1 - commo ratio ] =
1 [ 1 - 4^6] / [ 1 - 4 ] = 1365
8. Sum of the first seven terms is
6 [ 1 - (-4)^7 ] / [ 1 - (-4) ] =
6 [ 1 - (-4)^7 ] / 5 = 19662
9. Sum of 1st 10 terms =
12 [ 1 - 2^10] / [ 1 - 2 ] = 12276
