Question
An arithmetic series has first term -50 and common difference 4. How many terms are in the series so that the sum of the series first exceeds 100?
Answers
Again, use your definition.
you know S(n) = (n/2)(2a + (n-1)d ), so
(n/2)(2a + (n-1)d ) > 100
and you know both a and d
remember that n has to be a whole number, and you will end up with a quadratic inequality.
(n/2)(2a + (n-1)d ) = 100 ,
sub in your values, solve the resulting quadratic for n
<b>round up</b> your n to the next whole number
you know S(n) = (n/2)(2a + (n-1)d ), so
(n/2)(2a + (n-1)d ) > 100
and you know both a and d
remember that n has to be a whole number, and you will end up with a quadratic inequality.
(n/2)(2a + (n-1)d ) = 100 ,
sub in your values, solve the resulting quadratic for n
<b>round up</b> your n to the next whole number
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