Question

find a if d=-3 , n=12 , sn= -126

Answer 1

Step-by-step explanation:

we know that

Sn = n/2*(2a+(n-1)*d)

this,

126=12/2*(2a+(12-1)*3)

126=6*(2a+11*3)

126=6*(2a+33)

this gives,

2a+33=126/6

2a+33=21

2a=21-33

2a=-12

a= - 6 ans