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() // + + +-------- ++++--------------- + +++---------- ++++----------- - N N 1+2+3+4++10 n=10 =

, =55

- ? ? - , N = a+(n-1)d , a= , d= , n= = n

a= , d= n= , n = a+(n-1)d 111 N = {2a+(n-1)d}

2+4+6+ 30 , =2 d=4-2=2 n = a+(n-1)d or, 30=2+(n-1)2 or,30=2+2n-2 or,30=2n or,2n=30

or,n= =15Ans.

1+2+3+4+-----------+50=?1+3+5+7+ 29 = = =2551=1275 Ans. , n=a+(n-1)d or,29=1+(n-1)2 or,29=1+2n-2 or, 29=2n-1 or,2n=29+1 or,2n=30 or,n= =15Ans

N =a+(n-1)dN = {2a+(n-)d}4+6+8+-------+60=? , N = a+(n-1)d , a=4 d=6-4=2 n=? , 4+(n-1)2=60 or, 4+2n-2=60 or,2+2n=60 or,2n=60-2 or,n= =29 Ans

= {2a+(n-1)d}

= {24+(29-1)2} = {8+282} = (8+56)= 64=928 Ans.

N n 1+2+3+4+------------+100=?

1 n =a+(n-1)d

2 n = {2a+(n-1)d}

3 = = = 50 101 =5050 Ans.

,a=5 d=3 n=10