Question

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

	\(\sqrt{ }\)

 

Answer 1

\(\left(2+x\right)+\left(4+x\right)+\left(6+x\right)+...+\left(52+x\right)=780\)

\(\Leftrightarrow26x+\left(2+4+6+...+52\right)=780\)

\(\Leftrightarrow26x+\left[\left(52+2\right).26:2\right]=780\)

\(\Leftrightarrow26x+702=780\)

 \(\Leftrightarrow26x=78\)

\(\Leftrightarrow x=\frac{78}{26}=3\)

Answer 2

(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