Question

In , -25 an arithmetic sequence if 17 is the 3rd term, -25 is the 17th term then which term is -1 ?

• A. 8
• B. 10
• C. 11
• D. 9

Answer 1

Answer:

D. 9

$x_3=17;x_{17}=-25$

d= term difference / position difference

$d=\frac{-25-17}{17-3}$

$d=\frac{-42}{14}$

$d=-3$

$x_1=x_3-(3-1)d$

$x_1=17-2\times -3$

$x_1=17+6=23$

$x_1+(n-1)d=-1$

$23+(n-1)\times -3=-1$

$23-3n+3=-1$

$26-3n=-1$

$-3n=-1-26$

$-3n=-27$

$n=27/3=9$