a 128-3 (X+4)=23
b (12X-64)×8mũ3 =4×8 mũ4
tìm x biết a, 128 - 3 x ( x + 4 ) = 13 ; b , ( 12x - 4 ^ 3 ) x 8 ^3 = 4 x 8 ^ 4 ; c, [ ( 4x + 28 ) x 23 + 55 ] : 5 = 35
tìm x biết a, 128 - 3 x ( x + 4 ) = 13 ; b , ( 12x - 4 ^ 3 ) x 8 ^3 = 4 x 8 ^ 4 ; c, [ ( 4x + 28 ) x 23 + 55 ] : 5 = 35
a: =>3(x+4)=115
=>x+4=115/3
hay x=103/3
b: =>\(8^3\cdot\left(12x-64\right)=4\cdot8^4\)
\(\Leftrightarrow12x-64=32\)
=>12x=96
hay x=8
c: \(\Leftrightarrow\left(4x+28\right)\cdot23+55=175\)
=>(4x+28)x23=120
=>4x+28=120/23
=>4x=-524/23
hay x=-131/23
Tìm số tự nhiên x, biết:
a, 128 – 3( x + 4 ) = 23
b, [( 4x + 28 ).3 + 55] : 5 = 35
a) \(128-3\left(x+4\right)=23\)
\(\Rightarrow3\left(x+4\right)=128-23\)
\(\Rightarrow3\left(x+4\right)=105\)
\(\Rightarrow x+4=35\)
\(\Rightarrow x=35-4\)
\(\Rightarrow x=31\)
b) \(\left[\left(4x+28\right)\cdot3+55\right]:5=35\)
\(\Rightarrow\left(4x+28\right)\cdot3+55=35\cdot5\)
\(\Rightarrow\left(4x+28\right)\cdot3+55=175\)
\(\Rightarrow\left(4x+28\right)\cdot3=120\)
\(\Rightarrow4x+28=40\)
\(\Rightarrow4x=12\)
\(\Rightarrow x=3\)
a, \(128-3\left(x+4\right)=23\)
\(=>3\left(x+4\right)=128-23\)
\(=>3\left(x+4\right)=105\)
\(=>x+4=105:3\)
\(=>x+4=35\)
\(=>x=35-4\)
\(=>x=31\)
b, \(\left[\left(4x+28\right).3+55\right]:5=35\)
\(=>\left(4x+28\right).3+55=35.5\)
\(=>\left(4x+28\right).3+55=175\)
\(=>\left(4x+28\right).3=175-55\)
\(=>\left(4x+28\right).3=120\)
\(=>4x+28=120:3\)
\(=>4x+28=40\)
\(=>4x=40-28\)
\(=>4x=12\)
\(=>x=12:4\)
\(=>x=3\)
\(#WendyDang\)
a) 128 - 3 (x + 4) =23
3.( x + 4) = 128 -23
3. ( x + 4) = 105
x + 4 = 105 :3
x + 4 = 35
x = 35 -4
x = 31
4)Tinh GTBT
a)x^3 + 12x^2 + 48x + 64 khi x=6
b)x^3 - 6x^2 + 12x - 8 khi x=22
5)Tim x
a) (x+9)^3 = 27
b)8 - 12x - x^3 + 6x^2 = -64
Bài 4:
a, \(x^3+12x^2+48x+64=x^3+4x^2+8x^2+32x+16x+64\)
\(=x^2.\left(x+4\right)+8x.\left(x+4\right)+16.\left(x+4\right)\)
\(=\left(x+4\right).\left(x^2+8x+16\right)=\left(x+4\right).\left(x^2+4x+4x+16\right)\)
\(=\left(x+4\right).\left(x+4\right)^2=\left(x+4\right)^3\)(1)
Thay \(x=6\) vào (1) ta được:
\(\left(6+4\right)^3=10^3=1000\)
Vậy...........
b, \(x^3-6x^2+12x-8=x^3-2x^2-4x^2+8x+4x-8\)
\(=x^2.\left(x-2\right)-4x.\left(x-2\right)+4.\left(x-2\right)\)
\(=\left(x-2\right).\left(x^2-4x+4\right)=\left(x-2\right).\left(x^2-2x-2x+4\right)\)
\(=\left(x-2\right).\left(x-2\right)^2=\left(x-2\right)^3\)(2)
Thay \(x=22\) vào (2) ta được:
\(\left(22-2\right)^3=20^3=8000\)
Vậy.............
Chúc bạn học tốt!!!
Bài 2:
a, \(\left(x+9\right)^3=27=3^3\)
\(\Rightarrow x+9=3\Rightarrow x=-6\)
Vậy.........
b, \(8-12x-x^3+6x^2=-64\)
\(\Rightarrow-\left(x^3-6x^2+12x-8\right)=-64\)
\(\Rightarrow x^3-2x^2-4x^2+8x+4x-8=64\)
\(\Rightarrow x^2.\left(x-2\right)-4x.\left(x-2\right)+4.\left(x-2\right)=64\)
\(\Rightarrow\left(x-2\right).\left(x^2-4x+4\right)=64\)
\(\Rightarrow\left(x-2\right).\left(x^2-2x-2x+4\right)=64\)
\(\Rightarrow\left(x-2\right).\left(x-2\right)^2=64\)
\(\Rightarrow\left(x-2\right)^3=4^3\Rightarrow x-2=4\Rightarrow x=6\)
Vậy............
Chúc bạn học tốt!!!
4. Tính giá trị biểu thức
a) x3 + 12x2 + 48x + 64 khi x = 6
Ta có:
x3 + 12x2 + 48x + 64 =
= (x3 + 64) + (12x2 + 48x)
= (x3 + 43) + 12x(x + 4)
= (x + 4)(x2 - 4x + 42) + 12x(x + 4)
= (x + 4)(x2 - 4x + 16 +12x)
= (x + 4)(x2 + 8x + 16)
= (x + 4)(x + 4)2
= (x + 4)3
Thế x = 6 vào biểu thức vừa tìm, ta được:
(x + 4)3 = (6 + 4)3 = 103 = 1000
Vậy 1000 là giá trị của biểu thức x3 + 12x2 + 48x + 64 khi x = 6.
b) x3 - 6x2 + 12x - 8 khi x = 22
Ta có:
x3 - 6x2 + 12x - 8 =
= (x3 - 8) - (6x2 - 12x)
= (x3 - 23) - 6x(x - 2)
= (x - 2)(x2 + 2x + 22) - 6x(x - 2)
= (x - 2)(x2 + 2x + 4 - 6x)
= (x - 2)(x2 - 4x + 4)
= (x - 2)(x - 2)2
= (x - 2)3
Thế x = 22 vào biểu thức vừa tìm, ta được:
(x - 2)3 = (22 - 2)3 = 203 = 8000
Vậy 8000 là giá trị của biểu thức x3 - 6x2 + 12x - 8 khi x = 22.
5. Tìm x a) (x + 9)3 = 27 \(\Leftrightarrow\) (x + 9)3 = 33 \(\Leftrightarrow\) x + 9 = 3 \(\Leftrightarrow\) x = - 6 Vậy x = -6 b) 8 - 12x - x3 + 6x2 = -64 \(\Leftrightarrow\) (8 - x3) - (12x - 6x2) = -64 \(\Leftrightarrow\) (23 - x3) - 6x(2 - x) = -64 \(\Leftrightarrow\) (2 - x)(22 + 2x + x2) - 6x(2 - x) = -64 \(\Leftrightarrow\) (2 - x)(4 + 2x + x2 - 6x) = -64 \(\Leftrightarrow\) (2 - x)(x2 - 4x + 4) = -64 \(\Leftrightarrow\) -(x - 2)(x - 2)2 = -64 \(\Leftrightarrow\) -(x - 2)3 = -43 \(\Leftrightarrow\) x - 2 = 4 \(\Leftrightarrow\) x = 6 Vậy x = 6
1.tìm x
a,128-3.(x=4)=23 b,[(4x =28).3=55]:5=35
c,(12x-4^3).8^3=4.8^4 d,720 :[41-(2x-5)]=263.5
\(a,128-3.\left(x+4\right)=23\\ \Rightarrow3.\left(x+4\right)=105\\ \Rightarrow x+4=35\\ \Rightarrow x=31\\ b,\left[\left(4x+28\right).3+55\right]:5=35\\ \Rightarrow\left(4x+28\right).3+55=175\\ \Rightarrow4x+28.3=120\\ \Rightarrow4x+28=60\\ \Rightarrow4x=32\\ \Rightarrow x=8.\)
c) \(\left(12x-4^3\right).8^3=4.8^4\)
\(12x-64=4.8^4:8^3\)
\(12x-64=32\)
\(12x=32+64\)
\(12x=96\)
\(x=\dfrac{96}{12}\)
\(x=8\)
d) \(720:\left[41-\left(2x-5\right)\right]:5=35\)
\(720:\left(41-2x+5\right):5=35\)
\(720:\left(46-2x\right)=35.5\)
\(720:\left(46-2x\right)=175\)
\(46-2x=720:175\)
\(46-2x=\dfrac{144}{35}\)
\(2x=46-\dfrac{144}{35}\)
\(2x=\dfrac{1466}{35}\)
\(x=\dfrac{1466}{35}:2\)
\(x=\dfrac{733}{35}\)
Bài 2. Tìm x biết:
a, 128 - 3(x + 4) = 23 d, 720 : [41 - (2x - 5)] = 2 3 .5
b, [(4x + 28).3 + 55] : 5 = 35 e, 123 – 5.( x + 4 ) = 38
c, (12x - 4 3 ).8 3 = 4.8 4 g, ( 3x – 2 4 ) .7 3 = 2.7 4
a,
128-3x-12=23
3x=128-12-23
3x=93
x=93:3
= 31
b,
(12x+84+55):5=35
12x+84+55=35.5
12x+84+55=175
12x=175-55-84
12x=36
x=36:12
x=3
viết biểu thức x^3 + 12X^2 +48x +64 dưới dạng lập phương của một tổng là:
A.(x+4)^2
B.(x-4)^3
C.(x-8)^3
D.(x+8)^3
tìm x biết
x/4+x/8+x/32+x/64+x/128=63/128
a)2x – 12.4 = 28
b)128-3(x +4)= 23
c) 20 + 8.(x + 3) = 52 .4
d) (12x -4 3 ).83= 4.84
e) 720: [41-(2x-5)]=23 .5
f) (2x- 4)(x – 3) = 0
g) (2x +1)3= 5.25
h) 2 x . 4 = 128
i) 5x-2 = 1
k)2x + 2x + 3= 144
giúp me được ko