Toán Lớp 6: tìm x biết a.x-71=129 b.21-5.(x-4)=11 c.450:[41-(2x-5)]=3^2.5 d.3^x^+^2+3^x=10 e.(3x-5)^2=16

Question

Toán Lớp 6:  tìm x biết  a.x-71=129 b.21-5.(x-4)=11 c.450:[41-(2x-5)]=3^2.5 d.3^x^+^2+3^x=10 e.(3x-5)^2=16

ngoclankhue · Answer

$ text{a) x - 71 = 129 &hArr; x = 129 + 71 = 200}$   $ text{b) 21 - 5.( x -4 ) = 11}$   $ text{&hArr; 21 - 5x + 20 = 11}$   $ text{&hArr; -5x = 11 - 21 - 20}$   $ text{&hArr; -5x = -30 }$   $ text{&hArr; x = 6}$   $ text{c) 450: [ 41 - ( 2x - 5 ) ] = 3&sup2; . 5}$   $ text{&hArr; 450: ( 41 - 2x + 5 ) = 9. 5}$   $ text{&hArr; 450: ( 46 - 2x ) = 45 }$   $ text{&hArr; 46 - 2x = 450 : 45 }$   $ text{&hArr; 2( 23 - x ) = 10}$   $ text{&hArr; 23 - x = 5}$   $ text{&hArr; x = 23 - 5 }$   $ text{&hArr; x = 18}$   $ text{e) ( 3x - 5 )&sup2; = 16}$   $ text{&hArr; ( 3x - 5 )&sup2; = 4&sup2;}$   $ text{&hArr; 3x - 5 = 4}$   $ text{&hArr; 3x = 4 + 5}$   $ text{&hArr; 3x = 9}$   $ text{&hArr; x = 3 }$   $ text{CH&Uacute;C BẠN HỌC TỐT!!}$

truongankimtrong · Answer

a)x-71=129   x=129+71   x=200    b)21-5.(x-4)=11     5.(x-4)=21-11     5.(x-4)=10     x-4=10:5     x-4=2     x=2+4     x=6    c)450:[41-(2x-5)]=3^2. 5   450:[41-(2x-5)]=9.5   450:[41-(2x-5)]=45   41-(2x-5)=450:45   41-(2x-5)=10   2x-5=41-10   2x-5=31   2x=31+5   2x=36   x=36:2   x=18    e)(3x-5)^2=16     (3x-5)^2=4^2     =>3x-5=4     =>3x=6+4     =>3x=9     =>x=9:3     =>x=3