#)Giải :
\(S=2+4+6+...+2n=6972\)
\(\Rightarrow\frac{\left(2n+2\right)\left[\left(2n-2\right):2+1\right]}{2}=6972\)
\(\Rightarrow\frac{2\left(n+1\right)n}{2}=6972\)
\(\Rightarrow n\left(n+1\right)=6972\)
\(\Rightarrow n^2+n-6972=0\)
\(\Rightarrow\left(n+84\right)\left(n-83\right)=0\)
\(\Rightarrow n=83\)
#~Will~be~Pens~#
S=(2n+2)[(2n−2):2+1]2=6972S=(2n+2)[(2n−2):2+1]2=6972
⇒2(n+1)n2=6972⇒2(n+1)n2=6972
⇒n(n+1)=6972⇒n(n+1)=6972
⇒n2+n−6972=0⇒n2+n−6972=0
⇒(n+84)(n−83)=0⇒(n+84)(n−83)=0
⇒n=83⇒n=83 ( TM )
S=2+4+6+..+2n=6972
\(2\cdot\left(1+2+3+...+n\right)=6972\)
\(1+2+3+..+n=6972:2=3486\)
\(\left(n+1\right)\cdot n:2=3486\)
\(\left(n+1\right)\cdot n=6972\)
đến đây tự làm nha! Nhớ k cho mình nha
