Question

for ap s16=784 d=6 find a
​

Answer 1

Answer:

(i) S16=784

a=4

$$\begin{lgathered}s16 = \frac{16}{2} (2 \times 4 + (16 - 1)d) \\ 784 = 8(8 + 15d) \\ 98 = 8 + 15d \\ 90 = 15d \\ \huge \bold{16 = d}\end{lgathered}$$

(ii)S12=-78

d=-3

$$\begin{lgathered}s12 = \frac{12}{2} (2a + (12 - 1) - 3) \\ - 78 = 6(2a + 11( - 3) \\ - 13 = 2a - 33 \\ - 13 + 33 = 2a \\ 20 = 2a \\ \huge\bold{a = 10}\end{lgathered

hope it helpful please mark as brainlist