find the formula for an for the arithmetic sequence.
a3=94, a6=85
ok i know how to solve a similar problem when i am given a1 and d. but i dont have either A1 or d so how can i find them? to plug into an=dn+c and c= a1-d?? please help me understand this thank you.
Originally Posted by mathaddict
i don't know what you did but it made no sense to me. i actually figured it out. what i did was
a6-a3= 3 terms apart
a6=a3+3d--> 85=94+3d--> d=-3
an=a1+(n-1)d
94=a1+(3-1)-3-->a1=100
c=a1-d-->c=100-(-3)-->c=103
an=-3n+103=answer!!!!!!!
thank you very much for your time and help mathaddict! it was greatly Appreciated.
OK , your method works fine too .. Then you stick to your method to make things easier .i don't know what you did but it made no sense to me. i actually figured it out. what i did was
a6-a3= 3 terms apart
a6=a3+3d--> 85=94+3d--> d=-3
an=a1+(n-1)d
94=a1+(3-1)-3-->a1=100
c=a1-d-->c=100-(-3)-->c=103
an=-3n+103=answer!!!!!!!
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