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axelneel
Identify the 42nd term of an arithmetic sequence where a1 = -12 and a27 = 66
i keep coming up with 126 but my options are 70,72,111,114. PLEASE HELP
|dw:1372218335949:dw|
\[\large a_{n}= a_{1}+(n-1)d\]
find r and then just plug in that first equation
\[\large 66 =-12+(27-1)d \]\[\large 66= -12 +26d\]\[\large 78 = 26d\]\[\large d= 3\] \[\large a_{42} = -12 + 3(42-1)\]\[\large a_{42} = -12 + 123\]\[\large a_{42} = 111\]
i have no idea what i was doing wrong... but thank you