Question

If the 3rd and 13th terms of an A.P. are -40 and 0, find its 20th term.
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Answer 1

Answer:

t20=28

Step-by-step explanation:

given:t3=-40 ,t13=0, t20=?

tn=a+(n-1)d

t3=a+(3-1)d

-40=a+2d-----------1

t13=a+(13-1)d

0=a+12d-----------2

subtract equation 1and2

a+2d=-40

- a+12d=0

-10d=-40

10d=40

d=40

10

d=4

taking d=4 in equation 1

a+2×4=-40

a+8=-40

a=-40-8

a=-48

t20=-48+(20-1)4

=-48+19×4

=-48+76

t20=28