x + 15 : 5 = 7
x = ?
giải phương trình : 5(x -1)(x - 5)(x -3)(x -15)= 7x^2
[2x-(4-3x)/5]/15=[7x-(x-3)/2]/5-x+1
2x-4-3x/5/15=7x-x-3/2/5-x+1
Câu 15. Kết quả phân tích đa thức 6x 2 + 6xy + 7x + 7y thành nhân tử là :
A. (7x+y)(5x+y)
B. ( 3x +5 ) (x+y)
C. ( x+y ) ( 6x + 7)
D. ( 7x +6)( x + y)
1. 6x+x=5^11:5^9+3
2. 7x-x=5^21:5^19+3x4-1
3. 7x-2x=6^17:6^15+44:11
a) A = -3x(x-5) +3( x2 -4x) -3x-10
b) B = 4x( x2 -7x +2) – 4( x3 -7x2 +2x -5)
c) C = 5x( x2 – x) – x2( 5x-5) -15
d) D = 7( x2 -5x+3)- x( 7x-35) -14
e) E = x2 - 4x - x( x-4) -15
a, 3-x=x-5 b, 7x+21=0 c, 0,25x+1,5=0 d, 6,36-5,3x=0
e, 3x+1=7x-11 f, 15-4x=6x+5 g, 2(x+1)=3+2x
h, 3(1-x)+4x-3 = 0
a: =>-2x=-8
hay x=4
b: =>7x=-21
hay x=-3
c: =>0,25x=-1,5
hay x=-6
d: =>5,3x=6,36
hay x=6/5
e: =>-4x=-12
hay x=3
f: =>-10x=-10
hay x=1
g: =>2x+2-3-2x=0
=>-1=0(vô lý)
h: =>3-3x+4x-3=0
=>x=0
a,
\(3-x=x-5\\ \Leftrightarrow3x-x+5=0\Leftrightarrow2x+5=0\)
\(\Rightarrow x=-\dfrac{5}{2}\)
b, \(\Rightarrow x=-\dfrac{21}{7}=-3\)
c, \(\Leftrightarrow x=\left(0-1,5\right):0,25=-6\)
a. <=> 2x=8 hay x=4
b.<=> x= -21/7 = -3
c. <=> x= -1,5/ 0,25=-6
d. <=> x= -6,36/-5,3=1,2
e.<=> 4x=12 hay x= 3
f. <=> 10x = 10 hay x = 1
g. <=> 2x +2 = 3 + 2x
<=> 2=3 ( vô lí )
h.<=> 3 - 3x + 4x -3 =0
<=> x=0
Tìm gtnn, gtln của A= x^2+8x+15 B= 7x-x^2-5
1) \(A=x^2+8x+15=\left(x^2+8x+16\right)-1=\left(x+4\right)^2-1\ge-1\)
\(minA=-1\Leftrightarrow x=-4\)
2) \(B=7x-x^2-5=-\left(x^2-7x+\dfrac{49}{4}\right)+\dfrac{29}{4}=-\left(x-\dfrac{7}{2}\right)^2+\dfrac{29}{4}\le\dfrac{29}{4}\)
\(maxB=\dfrac{29}{4}\Leftrightarrow x=\dfrac{7}{2}\)
Ta có: \(A=x^2+8x+15\)
\(=x^2+8x+16-1\)
\(=\left(x+4\right)^2-1\ge-1\forall x\)
Dấu '=' xảy ra khi x=-4
Tìm x , biết:
a) (2x-15)5 = (2x-15)3
b) (7x-11)3 = (-3)2 . 15 + 208
Giúp mình nhanh nhé
a)
\(\left(2x-15\right)^5=\left(2x-15\right)^3\\ \Leftrightarrow\left(2x-15\right)^5-\left(2x-15\right)^3=0\\ \Leftrightarrow\left(2x-15\right)^3.\left[\left(2x-15\right)^2-1\right]=0\\ \Leftrightarrow\left[{}\begin{matrix}2x-15=0\\\left(2x-15\right)^2-1=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}2x-15=0\\\left(2x-15-1\right).\left(2d-15+1\right)=0\end{matrix}\right.\\\Leftrightarrow\left[{}\begin{matrix}2x-15=0\\2x-16=0\\2x-14=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{15}{2}\\x=8\\x=7\end{matrix}\right. \)
b) \(\left(7x-11\right)^3=\left(-3\right)^2.15+208\\ \Leftrightarrow\left(7x-11\right)^3=343=7^3\\ \Leftrightarrow7x-11=7\\ \Leftrightarrow x=\dfrac{18}{7}\)