Question

find the sum of(-11)+(-7)+(-3)+1+....to 12 terms​

Answer 1

Answer:

$a = - 11 \\ d = - 7 - ( - 11) = - 7 + 11 = 4 \\ n = 12 \\ \\ S_{n} = \frac{n}{2} (2a + (n - 1)d) \\ S_{12} = \frac{12}{2} (2 \times ( - 11) + (12 - 1)4) \\ S_{12} = 6( - 22 + (11)4) \\ S_{12} = 6( - 22 + 44) \\ S_{12} = 6(22) \\ \boxed{ \large S_{12} = \underline{ \underline{ 132}}}$