Question

[thuận Nguyễn thuận]

1+3+5+...+x=36

Answer 1

[HT.Phong (9A5)]

\(1+3+5+...+x=36\\\left[ \left(x-1\right):2+1\right]\cdot\left(x+1\right):2=36\\ \dfrac{x-1+2}{2}\cdot\dfrac{x+1}{2}=36\\ \dfrac{x+1}{2}\cdot\dfrac{x+1}{2}=36\\ \dfrac{\left(x+1\right)^2}{4}=36\\ \left(x+1\right)^2=36\cdot4=144\)

TH1: x + 1 = 12 => x = 11 

TH2: x + 1 = -12 => x = -13 

Vì: x phải lớn hơn 0 => x = 11 

Answer 2

[Nguyễn Hoàng Anh]

1+3+5+...+x =36

1+3+5+7+9+11 =36