Q19. Find the sum of the: (a) first 50 even numbers
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even number =2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46,48,50
l=a+(n-1)d
50=2+(n-1)2
50=2+2n-2
50=2n
n=25
Sn=n/2[2a+(n-1)d
Sn=25/2[2×2+(25-1)2
Sn=25/2[4+48]
Sn=25/2×50
Sn=25×25
Sn=625
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