Question

find the 12th term of given a.p -1,-4,-7 also find s10​

Answer 1

Answer:

a = -1 ,d = -4+1= -3

n = 12

a12 = -1+(12-1)(-3)

-1+11(-3)

-1-33 = -34

s10 = 10/2 (-2+(10-1)(-3))

5(-2-27)

5×(-29)

-145

Answer 2

Answer:

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Step-by-step explanation:

so here given ap is -1,-4,-7

where a=t1=-1

d=t2-t1

=-7-(-4)

d=3

now apply

tn=a+(n-)d

put n=12

therefore we get

t12=-1+(12-1)×(-3)

=-1+(11×(-3))

=-33-1

hence t12=-34

now using

sn=n/2×(2a+(n-1)d

put n=10 and substitute values of a and d in it

we get S10=-145