Question

Tìm x biết: (x+5)+(x+10)+(x+15)+.......+(x+60)= 450

Các bn giúp nhok song tử này vs nha!

cảm on các bn nhìu nham nhun

Answer 1

Có: (x+5)+(x+10)+(x+15)+.....+(x+60)=450

x+5+x+10+x+15+...+x+60=450

12.x + (5+10+15+...+60)=450

12.x + 390 = 450

\(\Rightarrow12.x=60\Rightarrow x=5\).

Vậy x = 5.

Answer 2

\(\left(x+5\right)+\left(x+10\right)+..+\left(x+60\right)=450\)

\(\Leftrightarrow\left(x+x+...+x\right)+\left(5+10+...+60\right)=450\)

\(\Leftrightarrow12x+\dfrac{\left(5+60\right).12}{2}=450\)

\(\Leftrightarrow12x+390=450\)

\(\Leftrightarrow x=5\)