a)-4, 8, -16, 32, -64.
This is a geometric series with a=-4 and r=-2
So the next terms are 128 and -256.
So series will continue as -4, 8, -16, 32, -64, 128, -256.
b) 1, 4, 20, 120, 840,...
The second term is multiplied by 4, the next one multiplied by 5, the next by 6 and so on so it follows:
840x8=6720, 6720x9=60480.
So the series will continue as follows 1, 4, 20, 120, 840, 6720, 60480.
c)3, 6, 12, 21, ...
The series is such that the difference is a AP, since 6-3=3,12-6=6, 21-12=9.
So the next term will be 21+12=33, the next is 33+15=48, so the series will continue as follows:
