it's a Arithmetic progression question
The 12th term of an AP is -28 and 18th term is -46 . Find it's first term and common difference?
Answers
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3
ANSWER
18
th
term fine
a= first term = -7 d= common diff = 5
general term
= a+(n-1)d
=-7+(18-1)5
=-7+85
= 78 Answer
II part
last term = 149 given in question
L = a+(n-1)d
149=a+(22-1)7
149=a+21×7
149=a+147
a=149-147
a=2
S=
2
n(a+L)
S=
2
22(2+149)
S=
2
22(151)
Sum = 1661
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