Question

If 21,a,b,-3 are in AP then find the value of a+b?
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Answer 1

Step-by-step explanation:

for an AP ,

nth term + (n+2)th term= 2* (n+1)th term

21,a,b are in AP so,

21+b =2a

b=2a-21

a,b,-3 are in AP so,

-3+a=2b

-3+a=2(2a-21)

-3+a=4a-42

3a=39

a=13

b=2a-21=5

a+b=13+5=18

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