Răspuns:
x = 265
Explicație pas cu pas:
4+13+22+......+x = 4035 <=>
(x+4)·[(x-4):9 +1]:2 = 4035 =>
(x+4)·[(x-4):9+⁹⁾1] = 8070 =>
(x+4)·(x-4+9):9 = 8070 =>
(x+4)·(x+5) = 8070·9 = 72630
x²+9x+20 - 72630 = 0 =>
x²+9x-72610 = 0 =>
x₁,₂ = (-9±√(81+290440) /2
x₁,₂ = (-9±√290521)/2
x₁,₂ = (-9±539)/2 ; x ∈ N =>
x = (-9+539)/2 = 530/2 => x = 265
4+13+22+.....+265 = (4+265)·(261:9 +1):2 =
= 269·15 = 4035 , corect.
#copaceibrainly
