Răspuns:
Explicație pas cu pas:
a)
x+1+x+2+.......+x+50=(x+25)²+25
50x+1+2+....+50=(x+25)²+25
50x+50×51/2=x²+50x+625+25
x²+650=25×51 x²=1275-650 x²=625 x=25
b)1+3+5+.....+(2x-1)=100
∑(2k-1)=100 2k(k+1)/2-k=100 k²+k-k-100=0 k²=100
k=10
