Tìm x : 2 + 4 + 6 + ... + 2 . x = 110

=> 2+4+6+8+...+2x=1102+4+6+8+...+2x=110

<=> (2x+2).�2=1102(2x+2).x​=110

<=> 2x.(x+1) = 2.110

=> x.(x+1) = 110

<=> x.(x+1) = 10.(10+1)

<=> x = 10