Question

Use the appropriate formula (and show work) to find a1 given that
S16 = -160 and a16 = -25

Answer 1

a1 = 5

Explanation:

1. Substitute S16 = -160 into the second formula.

2. solve as mush as possible

3. a16 is given. substitute.

4. solve

Answer 2

`a_1=5`

Explanation:

Given:

• 
  `S_(16)=-160`
• 
  `a_(16)=-25`

`\textsf{Use}\quad S_n=(n)/(2)(a_1+a_n):`

`\begin{aligned}S_(16) &=-160\\\implies S_(16)=(16)/(2)(a_1+a_(16)) &=-160\\\implies (16)/(2)(a_1+(-25)) & =-160\\8(a_1-25) &=-160\\a_1-25 &=-20\\a_1&=-20+25\\a_1 &=5\end{aligned}`