the first three terms of sequence are -2,4, & -8. if each subsequent term is the product of the preceding term how many of the first 90 terms are negative?

Question

thesmartone · Answer

Well it is going -, +, -, +

thesmartone · Answer

And it is being multiplied by -2...

thesmartone · Answer

look at the first 4
-2, 4, -8, 16

thesmartone · Answer

Its 2 positive and two negative...

thesmartone · Answer

So for 90 it would have to be 45 positive and 45 negative....

anonymous · Answer

u use any formula? @TheSmartOne

thesmartone · Answer

No just logic..

anonymous · Answer

no i can solve it in this but there must be some formula of airthmetictic progression or etc

anonymous · Answer

the formulas are "Un=(1st term)+(n-1)d" d=common difference n=# term for an arithmetic sequences and "Un=(1st term)*r^n-1" r=ratio (what the number is being multiplied by) in a geometric sequence    @rosebird

anonymous · Answer

@lexxygeorge  i have done with these formulas but not getting the answer.
one thing more what is the value of d?

anonymous · Answer

you would use the geometric formula for that problem and r=-2. but in general d= the common difference which is just what the number is being added or subtracted by.

anonymous · Answer

|dw:1415333057930:dw| not gettin correct answer from this @lexxygeorge