Question

AB = 2AC हैं।
A.P: 21, 18, 15...........का कौन सा पद -81
है?
प्र.20.
A.P.24, 21, 18............ के कितने पद लिए जाये कि योग 78 हो ​

Answer 1

for first question

AP : 21,18,15

so (a1) or (a) is 21

also, (d) is (18 -21) i.e. -3. (((an is -81)))

now to check that -81 is part of that AP

an = a + (n-1) d

-81 = 21 + (n-1) (-3)

-81-21 = (n-1) (-3)

-102/ -3 = (n-1)

34 = n-1

so (n) is 35

i.e -81 is 35th term of an AP i