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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 :
\(A=2.\left(-2\right)=-4\)
\(a)3\left(x-1\right)^2=75\)
\(\Leftrightarrow\left(x-1\right)^2=25\)
\(\Leftrightarrow\orbr{\begin{cases}\left(x-1\right)^2=\left(-5\right)^2\\\left(x-1\right)^2=5^2\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x-1=-5\\x-1=5\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x=-4\\x=6\end{cases}}\)
\(b)170+\left(84-5x\right):2^2=186\)
\(\Leftrightarrow\frac{84-5x}{4}=16\)
\(\Leftrightarrow84-5x=64\)
\(\Leftrightarrow5x=20\)
\(\Leftrightarrow x=4\)
\(c)125-5\left(x+4\right)=38\)
\(\Leftrightarrow5\left(x+4\right)=87\)
\(\Leftrightarrow x+4=\frac{87}{5}\)
\(\Leftrightarrow x=\frac{87}{5}-4\)
\(\Leftrightarrow x=\frac{67}{5}\)
Bài 1:
\(a,\left(a+b-c\right)-\left(b-c-d\right)\)
\(=a+b-c-b+c+d\)
\(=a+d\)
\(b,-\left(a-b+c\right)+\left(a-b+d\right)\)
\(=-a+b-c+a-b+d\)
\(=-c+d\)
\(c,\left(a+b\right)-\left(-a+b-c\right)\)
\(=a+b+a-b+c\)
\(=2a+c\)
\(d,-\left(a+b\right)+\left(a+b+c\right)\)
\(=-a-b+a+b+c\)
\(=c\)
Bài 3 :
\(a,15-\left(4-x\right)=6\)
\(4-x=15-6\)
\(4-x=9\)
\(x=4-9\)
\(x=-5\)
\(b,-30+\left(25-x\right)=-1\)
\(25-x=-1+30\)
\(25-x=29\)
\(x=25-29\)
\(x=-4\)
\(c,x-5=-1\)
\(x=-1+5\)
\(x=4\)
\(d,x-4=-10\)
\(x=-10+4\)
\(x=-6\)
\(e,x+3=-8\)
\(x=-8-3\)
\(x=-11\)
\(g,x+6=0\)
\(x=-6\)
Câu 1:
A, (a+b-c)-(b-c-d)
= a+b-c-b+c+d
= a+(b-b)+(c-c)
= a
B, -(a-b+c)+(a-b+d)
= -a+b-c+a+b+d
= (a-a)+(b+b)+d-c
= 2b+d-c
C, (a+b)-(-a+b-c)
= a+b+a-b+c
= (a+a)+(b-b)+c
= 2a+c
D, -(a+b)+(a+b+c)
= -a-b+a+b+c
= (-a+a)+(b-b)+c
= c
=
rút gọn dễ :))
\(a,-a-\left(b-a-c\right)\)
\(=-a-b+a+c\)
\(=-b+c\)
\(b,-\left(a-c\right)-\left(a-b+c\right)\)
\(=-a+c-a+b-c\)
\(=-2a+b\)
\(c,-\left(a-b+c\right)-\left(a+b+c\right)\)
\(=-a+b-c-a-b-c\)
\(=-2a-2c\)
\(\text{a, x + (-30) - [95 + (-40) + (-30)]}\)
\(x+\left(-30\right)-95+40+30\)
\(=x-95+40\)
\(=x-55\)
b, a + (273 - 120) - (270 - 120)
\(=a+273-120-270+120\)
\(=a+\left(273-270\right)+\left(-120+120\right)\)
\(=a+3\)
c, b - (294 + 130) + (94 + 130)
\(=b-294-130+94+130\)
\(=b+\left(-294+94\right)+\left(-130+130\right)\)
\(=b-200\)
2. Đơn giản biểu thức sau khi bỏ ngoặc:
a, -a - (b - a - c)
\(=-a-b+a+c\)
\(=\left(-a+a\right)-b+c\)
\(=-b+c\)
b, -(a - c ) - (a - b + c)
\(=-a+c-a+b-c\)
\(=\left(-a-a\right)+\left(c-c\right)+b\)
\(=-2a+b\)
c, -( a - b + c) - (a + b + c)
\(=-a+b-c-a-b-c\)
\(=\left(-a-a\right)+\left(b-b\right)+\left(-c-c\right)\)
\(-2a+-2c\)
học tốt !!
Rút gọn biểu thức
\(\text{a,x+(-30)-[95+(-40)+(-30)]}\)
\(=x+\left(-30\right)-95+40+30\)
\(=x-95+40=x-55\)
\(\text{a+(273-120)-(270-120)}\)
\(=a+273-120-270+120\)
\(=a+273-270=a+3\)
\(\text{b-(294+130)+(94+130)}\)
\(=b-294-130+94+130\)
\(=b-294+94=b-200\)
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 =)