How many terms of the AP 25,28,31,... are needed to give the sum 1070?
Answers
Answered by
7
given data is ,
Sn = 1070
a = 25
d = 28 - 25 = 3
n = ?
FORMULA : Sn = n/2 ( 2a + (n -1) d)
1070 = n/2 [ 2 x 25 + ( n - 1 ) 3 ]
1070 x 2 = n [ 50 + 3n - 3 ]
2140 = n ( 47 + 3n)
2140 = 47n + 3n^2
now solve this equation by the quadratic formula or middle term splitting...
Sn = 1070
a = 25
d = 28 - 25 = 3
n = ?
FORMULA : Sn = n/2 ( 2a + (n -1) d)
1070 = n/2 [ 2 x 25 + ( n - 1 ) 3 ]
1070 x 2 = n [ 50 + 3n - 3 ]
2140 = n ( 47 + 3n)
2140 = 47n + 3n^2
now solve this equation by the quadratic formula or middle term splitting...
dought full stap
dought full step
Answered by
8
No. of terms= 20
Hope this helps you...✌
Hope this helps you...✌
Attachments:
3n sq. + 47n - 2140 = 0
3n sq. + 60n - 107n - 2140 = 0 dought full step
3n sq. + 60n - 107n - 2140 = 0 dought full step
here as u its forming a quadratic equation
where a= 3 ,b= 47,c= 2140
u have to × (ac ) then factorise the resultant no. in such a way so that
either on adding or by subtraction u will get the result no. = ac
thanks
thanks
ur welcome
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3n sq. + 60n - 107n - 2140 = 0