A term in an arithmetic sequence and the common difference. Given #a_15=272# and d=20, how do you find the first three terms?

1 Answer
Dec 21, 2016

Answer:

#-8,12,32#

Explanation:

For the standard arithmetic sequence, the nth term is.

#color(red)(bar(ul(|color(white)(2/2)color(black)(a_n=a_1+(n-1)d)color(white)(2/2)|)))#
where #a_1" is first term"#

here #a_15=272" and " d=20#

and we want to find # a_1,a_2" and " a_3#

#rArr272=a_1+(14xx20)#

#rArra_1=272-280=-8#

#rArra_2=-8+d=-8+20=12#

#rArra_3=12+20=32#