Question

Last questions, plz help

Answer 1

Answer:

9. $a_n=7+6n$

10. $a_n=a_{n-1}+7$

Step-by-step explanation:

9. Given the sequence

$13, 19, 25, ...$

In this sequence,

$a_1=13\\ \\a_2=19\\ \\a_3=25\\ \\...$

Note that

$a_2-a_1=19-13=6\\ \\a_3-a_2=25-19=6,$

then the common difference in this sequence is $d=6$

You have

$a_1=13\\ \\d=6,$

then the explicit formula is

$a_n=a_1+(n-1)d\\ \\a_n=13+(n-1)\cdot 6\\ \\a_n=13+6n-6\\ \\a_n=7+6n$

10. Given the sequence

$-10,-3, 4, 11, ...$

In this sequence,

$a_1=-10\\ \\a_2=-3\\ \\a_3=4\\ \\a_4=11\\ \\...$

Note that

$a_2-a_1=-10-(-3)=-10+3=-7\\ \\a_3-a_2=-3-4=-7\\ \\a_4-a_3=11-4=7,$

then the common difference in this sequence is $d=7$

You have

$a_1=-10\\ \\d=7,$

then the recursive formula is

$a_n=a_{n-1}+d\\ \\a_n=a_{n-1}+7$