Question

1)
The number of team my is 638
Sum of
that of
in AP. is even
tems
even termo is 72 and last
term exceeds the first team by 16.5
the
Find ho. of
terms.​

Answer 1

Answer:

ANSWER

Let total no. of terms be 2n, & first term, a and comon diff be d.

a+(2n−1)d=l...........(1)

l−a=10.5

if we take odd terms only it will also be a A.P. of n terms only it will also be a A.P of n terms with common diff. of 2d.

24=n/2{2a+(n−1)2d}

24=n(a+(n−1)d)..........(2)

30=n/2{2(a+d)+(n−1)2d}

30=n(a+nd) .............. (3)

Put the value of equation (3) in equation (2)

24=30−nd

nd=6, putting in equation (1)

12−d=10.5

d=1.5 so n=4

a=1.5

so no of terms 8.

series 1.5,3,4.5,6,7.5,9,10.5,12

How satisfied are you with the answer?