Question

Plz do both of them for me and even show the work plzzzzzz

Answer 1

Answer:

(a)= option 3

(b)= option 3

Step-by-step explanation:

(A) It is given that a sequence is defined by the recursive function  $a_{1}=1$ and $a_{n}=a_{n-1}+n$

Now, substituting the value of n=2 in above equation,

$a_{2}=a_{1}+2$

$a_{2}=1+2$

$a_{2}=3$

Again putting n=3,

$a_{3}=a_{2}+3$

$a_{3}=3+3$

$a_{2}=6$

Putting n=4,

$a_{4}=a_{3}+4$

$a_{4}=6+4$

$a_{4}=10$

Putting n=5,

$a_{5}=a_{4}+5$

$a_{5}=10+5$

$a_{5}=15$

Putting n=6,

$a_{6}=a_{5}+6$

$a_{6}=15+6$

$a_{6}=21$

Putting n=7,

$a_{7}=a_{6}+7$

$a_{7}=21+7$

$a_{7}=28$

Hence, option 3 is correct.

(B) The given sequence is :

5, -10, 20, -40, 80.....

Since, the given sequence is GP, therefore

$a_{1}=5$ and r=-2

The nth term is given by:

$a_{n}=a_{1}r^{n-1}$

For fifteenth term, put n=15 in above equation, we get

$a_{15}=5(-2)^{14}$

=$5{\times}16384$

=$81920$

Hence, the fifteenth term is 81920.

Option 3 is correct.