ai nhanh tớ tích cho
\(1+3+5+...+\left(2x+1\right)=225\)
\(\left[\left(2x+1\right)+1\right].\left\{\left[\left(2x+1\right)-1\right]:2+1\right\}:2=225\)
\(2.\left(x+1\right).\left(x+1\right):2=225\)
\(\left(x+1\right)^2=225\)
\(\left(x+1\right)^2=15\)
\(\Rightarrow x+1=15\)
\(\Rightarrow x=14\)
mới dùng tích ntn
thx rất nhiều
