Respuesta :

ChoiSungHyun

Step-by-step explanation:

An = A + (n - 1)d

We have An = 81, d = -3 and n = 18.

Hence A = An - (n - 1)d = 81 - (17)(-3) = 132.

choccocakee
Substitute the given values into the equation


81= a+-3{18-1]


Solve the brackets


81= a-3[17]



81= a-51


Move 51 to the other side as a positive number


81+51 is 139


Therefore, a is equal to 139