Answer:
The sum of 12 terms of AP = -318
Explanation:
Points to remember
Sum of n terms of an AP
Sₙ = n/2[ 2a + (n - 1)d]
Where n - number of terms
a - first term
d - common difference
To find the sum of 12 terms
The given AP is 1, -4, -9, -14, . . .
a = 1, d= -5 and n = 12
Sₙ = n/2[ 2a + (n - 1)d]
= 12/2[2*1 + (12 - 1)*(-5)]
= 6[2 + (11*(-5))]
= 6[2 - 55]
= 6 * (-53)
= -318
The sum of 12 terms of AP = -318