tìm x -2/3.(x-1)-(x-1/3)=1/6 chúng minh rằng A=1/5+1/14+1/28+1/44+1/61+1/85+1/97<1/2 15/10/2021 Bởi Amaya tìm x -2/3.(x-1)-(x-1/3)=1/6 chúng minh rằng A=1/5+1/14+1/28+1/44+1/61+1/85+1/97<1/2
1. -2/3.(x-1)-(x-1/3)=1/6 =>-2/3x-(-2/3)-x-1/3=1/6 =>x(-2/3-1)+2/3 =1/6+1/3 =>x(-5/3)+2/3=1/2 =>x(-5/3)=1/2-2/3 =>x(-5/3)=-1/6 =>x=-1/6:-5/3 =>x=1/10 2.CMR A=1/5+1/14+1/28+1/44+1/61+1/85+1/97<1/2 A=1/5+(1/14+1/28+1/44)+(1/61+1/85+1/97)<1/2 A<1/5+(1/14×3)+(1/61×3) A<1/5+3/14+3/61 A<1/5+1/4+1/30=1/2 =>A<1/2 Bình luận
1.
-2/3.(x-1)-(x-1/3)=1/6
=>-2/3x-(-2/3)-x-1/3=1/6
=>x(-2/3-1)+2/3 =1/6+1/3
=>x(-5/3)+2/3=1/2
=>x(-5/3)=1/2-2/3
=>x(-5/3)=-1/6
=>x=-1/6:-5/3
=>x=1/10
2.CMR
A=1/5+1/14+1/28+1/44+1/61+1/85+1/97<1/2
A=1/5+(1/14+1/28+1/44)+(1/61+1/85+1/97)<1/2
A<1/5+(1/14×3)+(1/61×3)
A<1/5+3/14+3/61
A<1/5+1/4+1/30=1/2
=>A<1/2