t11=19 and t17=61.then what will be S12?
arithmetic series question
a+10d = 19
a+16d = 61
subtract them
6d = 42
d = 7
a + 70 = 19
a = -51
sum(12) = (12/2)(-102 + 11(7) ) = -150
arithmetic series question
a+16d = 61
subtract them
6d = 42
d = 7
a + 70 = 19
a = -51
sum(12) = (12/2)(-102 + 11(7) ) = -150