Question

Find the twentieth term if a36 = 78 and a42 = 90.

Answer 1

Hey are you there?

Answer 2

yes

Answer 3

are you given any other numbers?

Answer 4

like 1+2+3+..+..

Answer 5

that is all

Answer 6

helloo?

Answer 7

sorry i didnt see your post

Answer 8

ok so \[a _{n}=a _{1}+\left( n-1 \right)d\]

Answer 9

\[78=a _{1}+\left( 36-1 \right)d\]

\[78=a _{1}+35d\]

Answer 10

\[a _{1}=35d-78\]

Answer 11

\[90=a _{1}+\left( 42-1 \right)d\]

\[90=a _{1}+41d\]

\[90=\left( 35d-78 \right)+41d\]

Answer 12

solve for d, do you understand?

Answer 13

168=96d

168/96=d

Answer 14

humm....

Answer 15

wow i dont know that is confusing

Answer 16

\[a _{n}=a _{1}+(n-1)d\]
\[a _{20}=a _{1}+(20-1)d\]
\[a _{20}=a _{1}+19d\]
\[d=168/96\]

Answer 17

is that final answer

Answer 18

are you sure thats all your problem says?

Answer 19

yes