tìm x biết a, (3x+2) -(x-1) = 49x+1)
tìm x biết:
a, 49x^2 -4=0
b, (x+3)^2 - (x+2)(x-2)=11
c,(2x +1)^2 - (x-3)^2 - 3(x+5)(x-5) =5
d, (3x +1)(3x-1)=8
Giai giùm mình với
a/ Ta có : \(49.x^2-4=0\)
\(\Rightarrow49x^2=4\)
\(\Rightarrow x^2=\frac{4}{49}\Rightarrow\orbr{\begin{cases}x=\frac{-2}{7}\\x=\frac{2}{7}\end{cases}}\)
b/ \(\left(x+3\right)^2-\left(x+2\right)\left(x-2\right)=11\)
\(\left(x+3\right)\left(x+3\right)-\left(x+2\right)\left(x-2\right)=11\)
\(\Rightarrow\left(x^2+2.3.x+3^2\right)-\left(x^2-2^2\right)=11\)
\(\Rightarrow x^2+6x+9-x^2+4=11\)
\(\Rightarrow6x+13=11\)
\(\Rightarrow6x=11-13\)
\(\Rightarrow x=\frac{-2}{6}=\frac{-1}{3}\)
c/ \(\left(2x+1\right)^2-\left(x-3\right)^2-3\left(x+5\right)\left(x-5\right)=5\)
\(\Rightarrow\left(2x+1\right)\left(2x+1\right)-\left(x-3\right)\left(x-3\right)-3\left[\left(x+5\right)\left(x-5\right)\right]=5\)
\(\Rightarrow\left(4x^2+2.2x+1\right)-\left(x^2-2.3x+9\right)-3\left(x^2-25\right)\)\(=5\)
\(\Rightarrow\left(4x^2+4x+1\right)-\left(x^2-6x+9\right)-\left(3x^2-75\right)=5\)
\(\Rightarrow4x^2+4x+1-x^2+6x-9-3x^2+75=5\)
\(\Rightarrow\left(4x^2-x^2-3x^2\right)+\left(4x+6x\right)+\left(1-9+75\right)=5\)
\(\Rightarrow10x+67=5\)
\(\Rightarrow10x=5-67=-62\)
\(\Rightarrow x=\frac{-62}{10}=\frac{-31}{5}\)
d/ \(\left(3x+1\right)\left(3x-1\right)=8\)
\(\Rightarrow9x^2-1=8\)
\(\Rightarrow9x^2=8+1=9\)
\(\Rightarrow x^2=\frac{9}{9}=1\Leftrightarrow\orbr{\begin{cases}x=-1\\x=1\end{cases}}\)
Ai đó bấm hộ mình cái nút đúng đi!
Ta có : 49x2 - 4 = 0
=> 49x2 = 4
=> x2 = 196
=> x2 = 142 ; (-14)2
=> x = 14 ; -14
a) 49 . x2 - 4 = 0
49 . x2 = 4
7 2 . x2 = 22
(7 . x)2 = 22
7 . x = 2
x = 2 : 7
x = \(\frac{2}{7}\)
Tìm x,biết:
a) x^2-36=0
b) (3x-5)^2-(x+6)^2=0
c) (5x-4)^2-49x^2=0
d)4x^3-36x=0
e) 2/3x(x^2-4)=0
a) \(x^2-36=0\)
\(\Leftrightarrow x^2=36\)
\(\Leftrightarrow x=\pm\sqrt{36}=\pm6\)
b) \(\left(3x-5\right)^2-\left(x+6\right)^2=0\)
\(\Leftrightarrow\left(3x-5-x-6\right)\left(3x-5+x+6\right)=0\)
\(\Leftrightarrow\left(2x-11\right)\left(4x+1\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x=\frac{11}{2}\\x=\frac{-1}{4}\end{cases}}\)
d) \(4x^3-36x=0\)
\(\Leftrightarrow4x\left(x^2-9\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}4x=0\\x^2-9=0\end{cases}\Leftrightarrow\orbr{\begin{cases}x=0\\x=\pm3\end{cases}}}\)
Vậy...
tìm x a) 49x^2-1=0 b)(2x-1)^2-(4x+1)(x-3)=-3 c)9x(x-1)-(3x-1)^2=11 d) (2x+3)^2-(x-1)^2=0
no nooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooô
câu này biết mới vừa trao đổi bài với thầy xong nhưng ko biết đúng ko
a) \(49x^2-1=0\)
\(\Rightarrow\left(7x\right)^2-1^2=0\)
\(\Rightarrow\left(7x-1\right)\left(7x+1\right)=0\)
\(\Rightarrow\orbr{\begin{cases}7x-1=0\\7x+1=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=\frac{1}{7}\\x=\frac{-1}{7}\end{cases}}\)
b) \(\left(2x-1\right)^2-\left(4x+1\right)\left(x-3\right)=-3\)
\(\Rightarrow4x^2-4x+1-\left(4x^2-12x+x-3\right)=-3\)
\(\Rightarrow4x^2-4x+1-4x^2+12x-x+3=-3\)
\(\Rightarrow\left(4x^2-4x^2\right)+\left(-4x+12x-x\right)+4=-3\)
\(\Rightarrow7x+4=-3\)
\(\Rightarrow x=-1\)
c) \(9x\left(x-1\right)-\left(3x-1\right)^2=11\)
\(\Rightarrow\left(9x^2-9x\right)-\left(9x^2-6x+1\right)=11\)
\(\Rightarrow9x^2-9x-9x^2+6x-1-11=0\)
\(\Rightarrow-3x-12=0\)
\(\Rightarrow x=-4\)
d) \(\left(2x+3\right)^2-\left(x-1\right)^2=0\)
\(\Rightarrow\orbr{\begin{cases}\left(2x+3\right)^2=0\\\left(x-1\right)^2=0\end{cases}}\Rightarrow\orbr{\begin{cases}2x=-3\\x-1=0\end{cases}}\Rightarrow\orbr{\begin{cases}x=\frac{-3}{2}\\x=1\end{cases}}\)
Bài 1.khai triển HĐT
a,(3x-4)^2 b,(1+4x)^2 c,(2x+3)^3
d,(5-2x)^3 e,49x^2-25 f,1/25-81y^2
Bài 2.Tìm x biết:Viết đầy đủ
a,(x-5)^2-(x+7)(x-7)=8 b,(2x+5)^2-4(x+1)(x-1)=10
Bài 3.Tìm GTLN,GTNN của các biểu thức sau
a,A=x^2-6x+19 b,B=-x^2+8x-20
c,C=4x^2+12x+100 d,D=25+4x-x^2
Bài 1.
\(a, (3x-4)^2\)
\(=\left(3x\right)^2-2\cdot3x\cdot4+4^2\)
\(=9x^2-24x+16\)
\(b,\left(1+4x\right)^2\)
\(=1^2+2\cdot1\cdot4x+\left(4x\right)^2\)
\(=16x^2+8x+1\)
\(c,\left(2x+3\right)^3\)
\(=\left(2x\right)^3+3\cdot\left(2x\right)^2\cdot3+3\cdot2x\cdot3^2+3^3\)
\(=8x^3+36x^2+54x+27\)
\(d,\left(5-2x\right)^3\)
\(=5^3-3\cdot5^2\cdot2x+3\cdot5\cdot\left(2x\right)^2-\left(2x\right)^3\)
\(=125-150x+60x^2-8x^3\)
\(e,49x^2-25\)
\(=\left(7x\right)^2-5^2\)
\(=\left(7x-5\right)\left(7x+5\right)\)
\(f,\dfrac{1}{25}-81y^2\)
\(=\left(\dfrac{1}{5}\right)^2-\left(9y\right)^2\)
\(=\left(\dfrac{1}{5}-9y\right)\left(\dfrac{1}{5}+9y\right)\)
Bài 2.
\(a,\left(x-5\right)^2-\left(x+7\right)\left(x-7\right)=8\)
\(\Rightarrow x^2-2\cdot x\cdot5+5^2-\left(x^2-7^2\right)=8\)
\(\Rightarrow x^2-10x+25-\left(x^2-49\right)=8\)
\(\Rightarrow x^2-10x+25-x^2+49=8\)
\(\Rightarrow\left(x^2-x^2\right)-10x=8-25-49\)
\(\Rightarrow-10x=-66\)
\(\Rightarrow x=\dfrac{33}{5}\)
\(b,\left(2x+5\right)^2-4\left(x+1\right)\left(x-1\right)=10\)
\(\Rightarrow\left(2x\right)^2+2\cdot2x\cdot5+5^2-4\left(x^2-1^2\right)=10\)
\(\Rightarrow4x^2+20x+25-4x^2+4=10\)
\(\Rightarrow\left(4x^2-4x^2\right)+20x=10-25-4\)
\(\Rightarrow20x=-19\)
\(\Rightarrow x=\dfrac{-19}{20}\)
#\(Toru\)
Bài 1
a) (3x - 4)²
= (3x)² - 2.3x.4 + 4²
= 9x² - 24x + 16
b) (1 + 4x)²
= 1² + 2.1.4x + (4x)²
= 1 + 8x + 16x²
c) (2x + 3)³
= (2x)³ + 3.(2x)².3 + 3.2x.3² + 3³
= 8x³ + 36x² + 54x + 27
d) (5 - 2x)³
= 5³ - 3.5².2x + 3.5.(2x)² - (2x)³
= 125 - 150x + 60x² - 8x³
e) 49x² - 25
= (7x)² - 5²
= (7x - 5)(7x + 5)
f) 1/25 - 81y²
= (1/5)² - (9y)²
= (1/5 - 9y)(1/5 + 9y)
Bài 3.
\(a,A=x^2-6x+19\)
\(=x^2-6x+9+10\)
\(=\left(x^2-2\cdot x\cdot3+3^2\right)+10\)
\(=\left(x-3\right)^2+10\)
Ta thấy: \(\left(x-3\right)^2\ge0\forall x\)
\(\Rightarrow\left(x-3\right)^2+10\ge10\forall x\)
Dấu \("="\) xảy ra \(\Leftrightarrow x-3=0\Leftrightarrow x=3\)
Vậy: \(Min_A=10\) khi \(x=3\)
\(b,B=-x^2+8x-20\)
\(=-x^2+8x-16-4\)
\(=-\left(x^2-8x+16\right)-4\)
\(=-\left(x^2-2\cdot x\cdot4+4^2\right)-4\)
\(=-\left(x-4\right)^2-4\)
Ta thấy: \(\left(x-4\right)^2\ge0\forall x\)
\(\Rightarrow-\left(x-4\right)^2\le0\forall x\)
\(\Rightarrow-\left(x-4\right)^2-4\le-4\forall x\)
Dấu \("="\) xảy ra \(\Leftrightarrow x-4=0\Leftrightarrow x=4\)
Vậy \(Max_B=-4\) khi \(x=4\)
\(c,C=4x^2+12x+100\)
\(=4x^2+12x+9+91\)
\(=\left[\left(2x\right)^2+2\cdot2x\cdot3+3^2\right]+91\)
\(=\left(2x+3\right)^2+91\)
Ta thấy: \(\left(2x+3\right)^2\ge0\forall x\)
\(\Rightarrow\left(2x+3\right)^2+91\ge91\forall x\)
Dấu \("="\) xảy ra \(\Leftrightarrow2x+3=0\Leftrightarrow x=-\dfrac{3}{2}\)
Vậy \(Min_C=91\) khi \(x=\dfrac{-3}{2}\)
\(d,D=25+4x-x^2\)
\(=-x^2+4x-4+29\)
\(=-\left(x^2-2\cdot x\cdot2+2^2\right)+29\)
\(=-\left(x-2\right)^2+29\)
Ta thấy: \(\left(x-2\right)^2\ge0\forall x\)
\(\Rightarrow-\left(x-2\right)^2\le0\forall x\)
\(\Rightarrow-\left(x-2\right)^2+29\le29\forall x\)
Dấu \("="\) xảy ra \(\Leftrightarrow x-2=0\Leftrightarrow x=2\)
Vậy \(Max_D=29\) khi \(x=2\)
#\(Toru\)
A = -6x^2 + 3x - 1
B = -4x^2 +x
C = -49x^2 +3x-2
tìm x để biểu thức sau là phân số
1, x+1/(x+2)*(x+3)
2, x-2/3x^2+6x
3, 15-x/x*(x^2+4)
4, 49x/(x+1)^2
ai nhanh mình tích cho
tao vả bay lồn mày ấy hiểu chưa toán lớp 1 mà như cái phương chình đại học vậy hả thằng lồn ngu này
Tìm x : 49x^3=(3x+2)^2
1/Tính giá trị của biểu thức
a. x^2 + 6 x + 9 với x = 9997
b. x^3 - 12x^2 + 48 x-64 với x = 4
c. x^3 - 3x^2 + 3 x - 1 với x= 11
d. 49x^2 - 70x + 25 với x= 5
2/. Tìm x, biết
a. ( x+ 3 ) . (x^2 - 3x + 9 ) - x. ( x-1) .(x+1) = 14
b. (x+1 ) . (x^2 _x+1) - x. (x-3) . (x+3) =-27
c. 3.(x-1)^2 - 3x . (x-5 ) =1
d. (x-3) . (x^2+3x + 9) + x.(x+2)_ . (2_x) = 1
1/Tính giá trị của biểu thức
a. x^2 + 6 x + 9 với x = 9997
b. x^3 - 12x^2 + 48 x-64 với x = 4
c. x^3 - 3x^2 + 3 x - 1 với x= 11
d. 49x^2 - 70x + 25 với x= 5
2/. Tìm x, biết
a. ( x+ 3 ) . (x^2 - 3x + 9 ) - x. ( x-1) .(x+1) = 14
b. (x+1 ) . (x^2 _x+1) - x. (x-3) . (x+3) =-27
c. 3.(x-1)^2 - 3x . (x-5 ) =1
d. (x-3) . (x^2+3x + 9) + x.(x+2)_ . (2_x) = 1