Question

An ap has 15th and a common difference of -3 find the first and last term. If it. Sum is -120

Answer 1

confusing wording.
I interpret that to say, d = -3
sum(15) = -120

sum(15) = (15/2)(2a + 14(-3) ) = -120
15( 2a - 42) = -240
2a - 42 = -16
2a = 26
a = 13

<b>first term is 13
last term = term(15) = a+14d
= 13 + 14(-3) = -29</b>

check:
sum(15) = (15/2)(first + last)
= (15/2)(13 -29) = -120

Answer 2

wow - pretty garbled language. I will assume you meant

An a.p. has 15 terms and a common difference of -3. Find the first and last term if its sum is -120 .

S15 = 15/2 (2a+14d)
15/2 (2a+14(-3)) = 120
a = 29
a+14d = -13

Answer 3

Oops -- I missed the -120.

Answer 4

Good

Answer 5

How did u get ur 120

Answer 6

if it sum is 15 nko

Answer 7

Good