Câu 3 : (3 điểm) Tìm x N, biết:
a. (x-3)-75 = 16 c. 2x + 3 = 53 : 5
b. 2346 :(x+8) = 23 d. 3x+2 = 81
Tìm x biết:
a)3.(x-2)+2.(x-3)=5
b)(2x-8)2-16=0
c)(2x-1)2-(4x+1).(x-3)=3
a) \(3\left(x-2\right)+2\left(x-3\right)=5\)
\(\Rightarrow3x-6+2x-6=5\)
\(\Rightarrow5x=17\Rightarrow x=\dfrac{17}{5}\)
b) \(\left(2x-8\right)^2-16=0\)
\(\Rightarrow\left(2x-8-4\right)\left(2x-8+4\right)=0\)
\(\Rightarrow\left(2x-12\right)\left(2x-4\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}2x=12\\2x=4\end{matrix}\right.\)\(\Rightarrow\left[{}\begin{matrix}x=6\\x=2\end{matrix}\right.\)
c) \(\left(2x-1\right)^2-\left(4x+1\right)\left(x-3\right)=3\)
\(\Rightarrow4x^2-4x+1-4x^2+12x-x+3=3\)
\(\Rightarrow7x=-1\Rightarrow x=-\dfrac{1}{7}\)
a: Ta có: \(3\left(x-2\right)+2\left(x-3\right)=5\)
\(\Leftrightarrow3x-6+2x-6=5\)
\(\Leftrightarrow5x=17\)
hay \(x=\dfrac{17}{5}\)
b: Ta có: \(\left(2x-8\right)^2-16=0\)
\(\Leftrightarrow\left(2x-4\right)\left(2x-12\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=2\\x=6\end{matrix}\right.\)
a. \(3\left(x-2\right)+2\left(x-3\right)=5\)
\(\Leftrightarrow3x-6+2x-6=5\)
\(\Leftrightarrow5x=17\)
\(\Leftrightarrow x=\dfrac{17}{5}\)
b. \(\left(2x-8\right)^2-16=0\)
\(\Leftrightarrow\left(2x-8-4\right)\left(2x-8+4\right)=0\)
\(\Leftrightarrow4\left(x-6\right)\left(x-2\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-6=0\\x-2=0\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}x=6\\x=2\end{matrix}\right.\)
c. \(\left(2x-1\right)^2-\left(4x+1\right)\left(x-3\right)=3\)
\(\Leftrightarrow4x^2-4x+1-4x^2+11x+3-3=0\)
\(\Leftrightarrow7x+1=0\)
\(\Leftrightarrow x=-\dfrac{1}{7}\)
Câu III (2,0 điểm) Tìm x, biết:
a) x(x – 1) – x2 + 2x = 5
b) 2x2 – 2x = (x – 1)2
c) (x + 3)(x2 – 3x + 9) – x(x – 2)2 = 19
a) Ta có: \(x\left(x-1\right)-x^2+2x=5\)
\(\Leftrightarrow x^2-x-x^2+2x=5\)
hay x=5
b) Ta có: \(2x^2-2x=\left(x-1\right)^2\)
\(\Leftrightarrow2x\left(x-1\right)-\left(x-1\right)^2=0\)
\(\Leftrightarrow\left(x-1\right)\left(2x-x+1\right)=0\)
\(\Leftrightarrow\left(x-1\right)\left(x+1\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=1\\x=-1\end{matrix}\right.\)
c) Ta có: \(\left(x+3\right)\cdot\left(x^2-3x+9\right)-x\left(x-2\right)^2=19\)
\(\Leftrightarrow x^3+27-x\left(x^2-4x+4\right)-19=0\)
\(\Leftrightarrow x^3+8-x^3+4x^2-4x=0\)
\(\Leftrightarrow4x^2-4x+8=0\)(Vô lý)
Tìm số thực xx, biết:
a) 3√x<2x3<2 :
b) 3√2x−1>−3:2x−13>−3:
c) 3√2−3x≤1:2−3x3≤1:
d) 3√3−4x≥53−4x3≥5.
Bài 4: Tìm x, biết:
a) 3(2x – 3) + 2(2 – x) = –3 ; b) x(5 – 2x) + 2x(x – 1) = 13 ;
c) 5x(x – 1) – (x + 2)(5x – 7) = 6 ; d) 3x(2x + 3) – (2x + 5)(3x – 2) = 8 ;
e) 2(5x – 8) – 3(4x – 5) = 4(3x – 4) + 11; f) 2x(6x – 2x 2 ) + 3x 2 (x – 4) = 8.
\(a,3\left(2x-3\right)+2\left(2-x\right)=-3\\ \Leftrightarrow6x-9+4-2x=-3\\ \Leftrightarrow4x=2\\ \Leftrightarrow x=\dfrac{1}{2}\\ b,x\left(5-2x\right)+2x\left(x-1\right)=13\\ \Leftrightarrow5x-2x^2+2x^2-2x=13\\ \Leftrightarrow3x=13\\ \Leftrightarrow x=\dfrac{13}{3}\\ c,5x\left(x-1\right)-\left(x+2\right)\left(5x-7\right)=6\\ \Leftrightarrow5x^2-5x-5x^2-3x+14=6\\ \Leftrightarrow-8x=-8\\ \Leftrightarrow x=1\\ d,3x\left(2x+3\right)-\left(2x+5\right)\left(3x-2\right)=8\\ \Leftrightarrow6x^2+9x-6x^2-11x+10=8\\ \Leftrightarrow-2x=-2\\ \Leftrightarrow x=1\)
\(e,2\left(5x-8\right)-3\left(4x-5\right)=4\left(3x-4\right)+11\\ \Leftrightarrow10x-16-12x+15=12x-16+11\\ \Leftrightarrow-14x=-4\\ \Leftrightarrow x=\dfrac{2}{7}\\ f,2x\left(6x-2x^2\right)+3x^2\left(x-4\right)=8\\ \Leftrightarrow12x^2-4x^3+3x^3-12x^2=8\\ \Leftrightarrow-x^3-8=0\\ \Leftrightarrow-\left(x^3+8\right)=0\\ \Leftrightarrow-\left(x+2\right)\left(x^2-2x+4\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x=-2\\x\in\varnothing\left(x^2-2x+4=\left(x-1\right)^2+3>0\right)\end{matrix}\right.\)
Bài 4:
a: Ta có: \(3\left(2x-3\right)-2\left(x-2\right)=-3\)
\(\Leftrightarrow6x-9-2x+4=-3\)
\(\Leftrightarrow4x=2\)
hay \(x=\dfrac{1}{2}\)
b: Ta có: \(x\left(5-2x\right)+2x\left(x-1\right)=13\)
\(\Leftrightarrow5x-2x^2+2x^2-2x=13\)
\(\Leftrightarrow3x=13\)
hay \(x=\dfrac{13}{3}\)
c: Ta có: \(5x\left(x-1\right)-\left(x+2\right)\left(5x-7\right)=6\)
\(\Leftrightarrow5x^2-5x-5x^2+7x-10x+14=6\)
\(\Leftrightarrow-8x=-8\)
hay x=1
a/ \(3\left(2x-3\right)+2\left(2-x\right)=-3\)
\(\Leftrightarrow6x-9+4-2x=-3\)
\(\Leftrightarrow4x=2\)
\(\Leftrightarrow x=\dfrac{1}{2}\)
Vậy: \(x=\dfrac{1}{2}\)
===========
b/ \(x\left(5-2x\right)+2x\left(x-1\right)=13\)
\(\Leftrightarrow5x-2x^2+2x^2-2x=13\)
\(\Leftrightarrow3x=13\)
\(\Leftrightarrow x=\dfrac{13}{3}\)
Vậy: \(x=\dfrac{13}{3}\)
==========
c/ \(5x\left(x-1\right)-\left(x+2\right)\left(5x-7\right)=6\)
\(\Leftrightarrow5x^2-5x-5x^2+7x-10x+14=6\)
\(\Leftrightarrow-8x=-8\)
\(\Leftrightarrow x=1\)
Vậy: \(x=1\)
==========
d/ \(3x\left(2x+3\right)-\left(2x+5\right)\left(3x-2\right)=8\)
\(\Leftrightarrow6x^2+9x-6x^2+4x-15x+10=8\)
\(\Leftrightarrow-2x=-2\)
\(\Leftrightarrow x=1\)
Vậy: \(x=1\)
==========
e/ \(2\left(5x-8\right)-3\left(4x-5\right)=4\left(3x-4\right)+11\)
\(\Leftrightarrow10x-16-12x+15=12x-16+11\)
\(\Leftrightarrow-14x=-4\)
\(\Leftrightarrow x=\dfrac{2}{7}\)
Vậy: \(x=\dfrac{2}{7}\)
==========
f/ \(2x\left(6x-2x^2\right)+3x^2\left(x-4\right)=8\)
\(\Leftrightarrow12x^2-4x^3+3x^3-12x^2=8\)
\(\Leftrightarrow-x^3=8\)
\(\Leftrightarrow x=-2\)
Vậy: \(x=-2\)
Câu 3 (1,5 điểm). Tìm x, biết:
a) x + 2006 = 2021
b) 2x – 2016 = 24 x 4
c) 3(2x + 1)3 = 81
a: x=15
c: \(\Leftrightarrow2x+1=3\)
hay x=1
a) \(\Rightarrow x=2021-2006=15\)
b) \(\Rightarrow2x-2016=64\Rightarrow2x=2016+64=2080\Rightarrow x=1040\)
c) \(\Rightarrow\left(2x+1\right)^3=81:3=27\Rightarrow2x+1=3\)
\(\Rightarrow2x=3-1=2\Rightarrow x=1\)
`a) x= 15`
`b) 2x-2016=16\(\times\)4`
`⇔ 2x-2016=64`
`⇔ 2x= 2080`
`⇔ x= 1040`
`c) 3(2x+1)^3 =81`
`⇔ (2x+1)^3 =27`
`⇔ (2x+1)^3 =3^3`
`⇔ 2x+1=3`
`⇔ x= 1`
Bài 4. Tìm x ∈ N biết:
a) x3 = 27 b) (2x – 1)3 = 8
c) (2x – 3)2 = 9 d) 2x + 5= 3^4 : 3^2
3^4 tức là 3 mũ 4
a, x= 3
b, ko có x thỏa mãn
c, x= 3
d, x= 2
a: x=3
b: \(2x-1=2\)
hay \(x=\dfrac{3}{2}\)
c: \(\Leftrightarrow\left[{}\begin{matrix}2x-3=3\\2x-3=-3\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=0\end{matrix}\right.\)
bài 1: tìm x thuộc z
a) 3x + 5 = -22
b)3x - 5 = 35 - 5x
c) 2x -17 = -(3x - 18)
d) 8 ( x - 25 ) = 0
e) ( x + 3 ).( 5 - x ) = 0
g) 11 - ( -53 + x ) = 97
bài 2:Thực hiện các phép tính sau 1 cách hợp lí
a) - 2003 + ( - 21 + 75 + 2003 )
b) 1252 - ( 376 + 1252 ) + ( - 75 + 376 )
c) 43. ( 53 - 81 ) + 53 ( 81 - 43 )
dẫu . là dấu nhân nha mn.
mong mn giải giúp mình mình đang cần gấp
Tìm x, biết:
a, x(x -1) - x^2 + 2x = 5
b, 2x(3x + 4) -6x^2 = 16
a) PT \(\Leftrightarrow x^2-x-x^2+2x=5\) \(\Rightarrow x=5\)
Vậy ...
b) PT \(\Leftrightarrow8x=16\) \(\Rightarrow x=2\)
Vậy ...
a: Ta có: \(x\left(x-1\right)-x^2+2x=5\)
\(\Leftrightarrow x^2-x-x^2+2x=5\)
hay x=5
b: Ta có: \(2x\left(3x+4\right)-6x^2=16\)
\(\Leftrightarrow6x^2+8x-6x^2=16\)
\(\Leftrightarrow8x=16\)
hay x=2
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Bài 7:Tìm số nguyên x biết: a) 6:(x + 2) b) (x +13):(x +8) c) (3x + 2):(x −3) d) 3x+9:2x+1. |
b: \(\Leftrightarrow x+8\in\left\{1;-1;5;-5\right\}\)
hay \(x\in\left\{-7;-9;-3;-13\right\}\)