How do you find the first term of the arithmetic sequence given an = 48, Sn = 546, n = 26?

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Answer 1 · 2015-08-31T07:02:05

# a_1=color(blue)(-6#

We are provided with:
#a_N =48#
#S_n=546#
#n=26#

The formula for sum of an Arithmetic Sequence when the sum #s_n#, number of terms #n# and last term #a_n# are given is:

# color(blue)(S_n = (n/2)(a_1+a_n)#

# 546= 26 /2 (a +48)#

# 546*2/26= a+48#

# 21*2= a+48#

#a_1=42-48#

# a_1=color(blue)(-6#