Question

in an ap given a¹² =-41 ,d=-5 find a and s ¹²​

Answer 1

t12= -41

d = -5

tn = a + (n - 1)d

-41 = a + (12 - 1)(-5)

-41 = a + (11)(-5)

-41 + 55 = a

14 = a

•°• a = t1 = 14

sn = n/2[ 2a + (n - 1)d]

s12 = 12/2 [2 × 14 + (12 - 1)(-5)]

s12 = 6[28 + 11(-5)]

s12 = 6(28 - 55)

s12 = 6(-27)

s12 = -162