Two APS have the same first and last terms. The AP has 21 terms with a common difference of 9.How many terms has the other AP if its common difference is 4?

10 answers

First AP: first term --- a, d = 9, n = 21
last term is a + 20(9) = a + 180

Second AP: first term --- a, d = 4,
last term = a+4(n-1)
But a+4(n-1) = a+180
4n - 4 = 180
4n = 184
n = 46

check:
first sequence has last term of a + 180
2nd sequence has last term of a + 4(45) = a + 180

Note, the solution is independent of the value of a
i.e. you can make a equal to anything you want.

Because we obey him

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Love dis

first AP= un=a+(n-1)d
=a+(21-1)9
=a+(20)9
a =180
2nd AP=180+(n-1)4
=180+4n-4
=180-4,
am confused

Yes

Am confused

Am very confused

how is Un now 180