Question

D = 1 + 2 + 3 + 4 + 5 +...+ X = 500500

Answer 1

1+2+3+...+X=500500

=>\(\dfrac{\left(x-1\right)+1\cdot\left(1+x\right)}{2}\)=500500

=>x\(\cdot\)(x+1)=500500x2=1001000=1000x1001

=>x=1000.