típ nha m.n18) (2+x ) +(4+x)+(6+x )+...+(52+x) = 780(1/3.5 +1/5.7+1/7.9 +...+1/19.21).x = 9/720) (x+1)+(x+2)+...+(x+100)=575022) (x+1/1.3)+(x.1/3.5)+(x+1/5.7)+...+(x+23.25)= 11.x+(1/3+1/9+1/27+1/81+1/243 )23) (1/1.2.3 +1/2.3.4+....+1/8.9.10).x= 23/45 \(\sqrt{...
Đọc tiếp
típ nha m.n
18) (2+x ) +(4+x)+(6+x )+...+(52+x) = 780
(1/3.5 +1/5.7+1/7.9 +...+1/19.21).x = 9/7
20) (x+1)+(x+2)+...+(x+100)=5750
22) (x+1/1.3)+(x.1/3.5)+(x+1/5.7)+...+(x+23.25)= 11.x+(1/3+1/9+1/27+1/81+1/243 )
23) (1/1.2.3 +1/2.3.4+....+1/8.9.10).x= 23/45
| \(\sqrt{ }\) | |||||||
\(\left(2+x\right)+\left(4+x\right)+\left(6+x\right)+...+\left(52+x\right)=780\)
\(\Leftrightarrow26x+\left(2+4+6+...+52\right)=780\)
\(\Leftrightarrow26x+\left[\left(52+2\right).26:2\right]=780\)
\(\Leftrightarrow26x+702=780\)
\(\Leftrightarrow26x=78\)
\(\Leftrightarrow x=\frac{78}{26}=3\)
(2+x)+(4+x)+(6+x)+...+(52+x)=780
⇔26x+(2+4+6+...+52)=780
⇔26x+[(52+2).26:2]=780
⇔26x+702=780
⇔26x=78
⇔x=7826 =3