Question

14. Find the 20th term from the end of AP. a, a +d, a +2d,...,a+(n-1) d.
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Answer 1

Step-by-step explanation:

Given A.P is a,a+d,a+2d,a+3d,....

hence the common difference is given by d=an+1−an

by putting n=1 in above equation

d=a2−a1=(a+d)−(d)

d=d

first term of this A.P is

a1=a

the nth term of this A.P is given by

an=a1+(n−1)d

⟹an=a+(n−1)d….eq(1)

1) For finding the 30th term of sequence (a30)  put n=30 in eq(1)

⟹a30=a+(30−1)d

⟹a30=a+29d

2) For finding the 20th term  of sequence (a20) put n=20 in eq(1)

⟹a20=a+(20−1)

⟹a20=a+19d

now, 

a30−