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\(a)3\left(x-1\right)^2=75\)
\(\Leftrightarrow\left(x-1\right)^2=25\)
\(\Leftrightarrow\orbr{\begin{cases}\left(x-1\right)^2=\left(-5\right)^2\\\left(x-1\right)^2=5^2\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x-1=-5\\x-1=5\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x=-4\\x=6\end{cases}}\)
\(b)170+\left(84-5x\right):2^2=186\)
\(\Leftrightarrow\frac{84-5x}{4}=16\)
\(\Leftrightarrow84-5x=64\)
\(\Leftrightarrow5x=20\)
\(\Leftrightarrow x=4\)
\(c)125-5\left(x+4\right)=38\)
\(\Leftrightarrow5\left(x+4\right)=87\)
\(\Leftrightarrow x+4=\frac{87}{5}\)
\(\Leftrightarrow x=\frac{87}{5}-4\)
\(\Leftrightarrow x=\frac{67}{5}\)
Lời giải:
b.
$B=-(a-c)-(a-b+c)=-a+c-a+b-c=(-a-a)+(c-c)+b=-2a+0+b=-2a+b$
c.
$C=-(15-x)+5=-15+x+5=(-15+5)+x=-10+x$
d.
$D=[a+(a+3)]-[(a+2)-(a-2)]$
$=(2a+3)-(a+2-a+2)=(2a+3)-4=2a+3-4=2a-1$
Bài 1:
\(A=\dfrac{-1}{3}+1+\dfrac{1}{3}=1\)
\(B=\dfrac{2}{15}+\dfrac{5}{9}-\dfrac{6}{9}=\dfrac{2}{15}-\dfrac{1}{9}=\dfrac{18-15}{135}=\dfrac{3}{135}=\dfrac{1}{45}\)
\(C=\dfrac{-1}{5}+\dfrac{1}{4}-\dfrac{3}{4}=\dfrac{-1}{5}-\dfrac{1}{2}=\dfrac{-7}{10}\)
Bài 2:
a: \(=\dfrac{1}{5}+\dfrac{1}{2}+\dfrac{2}{5}-\dfrac{3}{5}+\dfrac{2}{21}-\dfrac{10}{21}+\dfrac{3}{20}\)
\(=\left(\dfrac{1}{5}+\dfrac{2}{5}-\dfrac{3}{5}\right)+\left(\dfrac{2}{21}-\dfrac{10}{21}\right)+\left(\dfrac{1}{2}+\dfrac{3}{20}\right)\)
\(=\dfrac{-8}{21}+\dfrac{13}{20}=\dfrac{113}{420}\)
b: \(B=\dfrac{21}{23}-\dfrac{21}{23}+\dfrac{125}{93}-\dfrac{125}{143}=\dfrac{6250}{13299}\)
Bài 3:
\(\dfrac{7}{3}-\dfrac{1}{2}-\left(-\dfrac{3}{70}\right)=\dfrac{7}{3}-\dfrac{1}{2}+\dfrac{3}{70}=\dfrac{490}{210}-\dfrac{105}{210}+\dfrac{9}{210}=\dfrac{394}{210}=\dfrac{197}{105}\)
\(\dfrac{5}{12}-\dfrac{3}{-16}+\dfrac{3}{4}=\dfrac{5}{12}+\dfrac{3}{16}+\dfrac{3}{4}=\dfrac{20}{48}+\dfrac{9}{48}+\dfrac{36}{48}=\dfrac{65}{48}\)
Bài 4:
\(\dfrac{3}{4}-x=1\)
\(\Rightarrow-x=1-\dfrac{3}{4}\)
\(\Rightarrow x=-\dfrac{1}{4}\)
Vậy: \(x=-\dfrac{1}{4}\)
\(x+4=\dfrac{1}{5}\)
\(\Rightarrow x=\dfrac{1}{5}-4\)
\(\Rightarrow x=-\dfrac{19}{5}\)
Vậy: \(x=-\dfrac{19}{5}\)
\(x-\dfrac{1}{5}=2\)
\(\Rightarrow x=2+\dfrac{1}{5}\)
\(\Rightarrow x=\dfrac{11}{5}\)
Vậy: \(x=\dfrac{11}{5}\)
\(x+\dfrac{5}{3}=\dfrac{1}{81}\)
\(\Rightarrow x=\dfrac{1}{81}-\dfrac{5}{3}\)
\(\Rightarrow x=-\dfrac{134}{81}\)
Vậy: \(x=-\dfrac{134}{81}\)
Tính giá trị biểu thức a - b - c biết :
a) a = 45, b= 175, c = -130.
\(\Rightarrow a-b-c=45-175-\left(-130\right)=0\)
b) a = -350, b = -370 c = 85.
\(\Rightarrow a-b-c=\left(-350\right)-\left(-370\right)-85=-65\)
c) a = -720, b = -370, c = -250.
\(\Rightarrow a-b-c=\left(-720\right)-\left(-370\right)-\left(-250\right)=-100\)
d) Cho biểu thức : A = ( -a - b+ c ) - ( -a - b - c ). Rút gọn A. Tính giá trị của A khi a = 1 ; b = -1 ; c= -2
Ta có : \(A=\left(-a-b+c\right)-\left(-a-b-c\right)\)
\(A=-a-b+c+a+b+c\)
\(A=\left(-a+a\right)+\left(-b+b\right)+\left(c+c\right)\)
\(A=2c\)
Thay c= -2 vào biểu thức A ta có :
\(A=2.\left(-2\right)=-4\)
a. x + 16 = a
=> x = a - 16
b. a - x = -186
=> x = a - (-186)
=> x = a + 186
c. b + x = a
=> x = a - b
d. b - x = a
=> x = b - a
a. x + 16 = a
=> x = a - 16
b. a - x = -186
=> x = a - (-186)
=> x = a + 186
c. b + x = a
=> x = a - b
d. b - x = a
=> x = b - a
\(D=\left(a+b-c\right)-\left(a-b+c\right)+\left(b+c-a\right)-\left(a-b-c\right)\)
\(D=a+b-c-a+b-c+b+c-a-a+b+c\)
\(D=\left(a-a-a-a\right)+\left(b+b+b+b\right)+\left(c+c-c-c\right)\)
\(D=4b-3a\)
a) \(x+\left(-10\right)-\left[87+\left(-41\right)+\left(-20\right)-x\right]\)
\(=x-10-\left(87-41-20-x\right)=x-10-87+41+20+x\)
\(=\left(x-x\right)+\left(20-10\right)-\left(87-41\right)=10-46=-36\)
b) \(a+\left(250-186\right)-\left(270-186\right)=a+250-186-270+186\)
\(=a+\left(250-270\right)+\left(186-186\right)=a-20\)
c) \(b-\left(393+170\right)+\left(93+170\right)=b-393-170+93+170\)
\(=b+\left(170-170\right)-\left(393-93\right)=b-300\)
d) \(-\left(a-b+c\right)-\left(a+b+c\right)=-a+b-c-a-b-c=-2a-2c\)
@Vũ Cao Minh⁀ᶦᵈᵒᶫ Phèn=)
Cảm ơn nhìu lắm =)