<p>If the first term of a sequence is 2, the second term is -4, third is 8, fourth is -16, 5th is -32, what is the 19th term value be? what is the 20th term value be?</p>
<p>so your equation is f(n)= (-1)(-2)^n… plug in a 19, plug in a 20, whatever :p</p>
<p>what is -1 there?</p>
<p>it adjusts for the fact that the first term is positive, second term negative, etc.</p>
<p>^^^the equation selter gave is slightly wrong. (-1) times [(-2)^n]</p>
<p>lol, it’s not wrong at all. order of operations.</p>
<p>I might be missing something, but shouldn’t -32 be +32?</p>
<p>@Azum… yeah, i’m pretty sure it’s a typo :p</p>
<p>yeah it’s a typo.
But hey selter, why don’t we just do (-16) (-2) ^ ([19 or 20]-4]</p>
<p>I would just have done 2^19 [or 2^20] and then figured out whether it was positive or negative based on a pattern [in this case, the odd-numbered terms, like the 19th term, are positive and the even terms are negative].</p>
<p>but what makes sense to me is often convoluted to other people…</p>