1. ## geometric progression?

Given a series a1, a2, a3, ……. an. If a1 = 25 and every term in the series is ‘-2’ times its previous number, then which column is larger?
Col A: a100
Col B: -10,000

Is this a geometric progression? So, we would use the formula an=ar^(n-1)=25(-2)^-99. This is much less than -10,000. So B is larger.

2. why 25(-2)^-99?

why for the minus before 99?

3. err sorry....its 25(-2)^99

4. 2^10=1024

so 2^99=very huge number...

5. Originally Posted by Also sprach Zarathustra
2^10=1024

so 2^99=very huge number...
$\displaystyle{25\cdot2^{99}>10000\implies 25\cdot(-2)^{99}<-10000}$