in an AP the first term is 22 the common difference is -4 and the sum of n terms is 64 find n explain double answer
Answers
Answered by
20
a=22
d= - 4
Sn=64
=>n/2{2a + (n-1_d} = 64
=> n/2 {2*22 +(n-1) * (-4)} = 64
=> n/2{44 - 4n +4} = 64
=> n*4{11-n+1} = 64*2
=> 11n - n sq. + n = 128/4
=> - n sq. + 11n + n = 32
=> - n sq. +12n - 32 = 0
=> n sq. - 12n + 32 = 0
=>n sq. - 4n - 8n +32= 0
=> n (n-4) - 8 ( n - 4 ) = 0
=>(n-4) (n-8) = 0
either n= 4 or n=8
double ans is possible because the sum of the terms from 5 to 8 will be 0.
kaira1818:
the sum of the first 8 terms = 22 + 18 + 14+10+6+2+(-2)+(-6) = 64
two answers are possible bcoz the sum of the terms frm 5th to 8th will be zero. This is becoz a is +ve and d is -ve, so tyhe terms will be +ve and some others -ve anbd will cancel out each other
can you understand??
amazing sir
a lot of thanks
how to mark it barinly
there is no option to mark it brainlist
u can mark me brainliest...u can see it near my ans
not showing sir
wait for sometime...let someone else ans anything ....then u can see the brainliest option and mark me as brainliest
Answered by
9
Answer:
Step-by-step explanation:
a=22
d= - 4
Sn=64
=>n/2{2a + (n-1_d} = 64
=> n/2 {2*22 +(n-1) * (-4)} = 64
=> n/2{44 - 4n +4} = 64
=> n*4{11-n+1} = 64*2
=> 11n - n sq. + n = 128/4
=> - n sq. + 11n + n = 32
=> - n sq. +12n - 32 = 0
=> n sq. - 12n + 32 = 0
=>n sq. - 4n - 8n +32= 0
=> n (n-4) - 8 ( n - 4 ) = 0
=>(n-4) (n-8) = 0
either n= 4 or n=8
Similar questions