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15 - 2x = 11
=> 2x = 15 - 11
=> 2x = 4
=> x = 4 : 2 = 2
3.(x - 9) + 15 = 81
=> 3x - 27 = 81 - 15
=> 3x - 27 = 66
=> 3x = 66 + 27
=> 3x = 93
=> x = 93 : 3 = 31
a) 15 - 2.x = 11
2.x = 4
x = 2
b) 3. (x - 9) + 15 = 81
3. (x - 9) = 66
x - 9 = 22
x = 31
c) (x+1)+(x+2)+...+(x+10)= 105
(x+x+....+x) + (1+2+....+10) = 105
x . 10 + 55 = 105
x . 10 = 50
x = 5
a) 5 - x = 17 - (-5)
5 - x = 22
x = 5 - 22
x = - 17
Vậy x = -17
b) x - 12 = - 9 - (-15)
x - 12 = 6
x = 6 + 12
x = 18
Vậy x = 18
c) 9 + 25 = (-7-x) - ( 25 - 7 )
34 = (-7-x) - 18
hay (-7-x) - 18 = 34
-7-x = 34 + 18
-7-x = 52
x = -7 - 52
x = - 59
Vậy x = -59
d) 11 + (15-11) = x - (25 - 9)
11 + 4 = x - 16
15 = x - 16
hay x - 16 = 15
x = 15 + 16
x = 31
Vậy x = 31
Nhớ lời bn nói nha ^ ^
B1:
Ta có: \(\frac{4^6.9^5+6^9.120}{8^4.3^{12}-6^{11}}=\frac{2^{12}.3^{10}-2^9.3^9.2^3.3.5}{2^{12}.3^{12}-2^{11}.3^{11}}\)
\(=\frac{2^{12}.3^{10}-2^{12}.3^{10}.5}{2^{12}.3^{12}-2^{11}.3^{11}}=\frac{2^{12}.3^{10}.\left(1-5\right)}{2^{11}.3^{11}.\left(2.3-1\right)}\)
\(=\frac{2.\left(-4\right)}{3.5}=-\frac{8}{15}\)
B2:
Ta có: \(1+3+5+...+x=1600\)
\(\Leftrightarrow\frac{\left(x+1\right)\cdot\left(\frac{x-1}{2}+1\right)}{2}=1600\)
\(\Leftrightarrow\left(x+1\right)\cdot\frac{x+1}{2}=3200\)
\(\Leftrightarrow\left(x+1\right)^2=6400\)
Xét theo dãy tăng tiến ta thấy được giá trị của x càng tăng
=> x dương => x + 1 dương
\(\Rightarrow x+1=80\)
\(\Rightarrow x=79\)
\(\left(2x+1\right)^3=-125\)
\(< =>\left(2x+1\right)^3=\left(-5\right)^3\)
\(< =>2x+1=-5\)
\(< =>2x=-5-1=-6\)
\(< =>x=-\frac{6}{2}=-3\)
Bài làm:
a) \(\left(2x+1\right)^3=-125\)
\(\Leftrightarrow\left(2x+1\right)^3=\left(-5\right)^3\)
\(\Rightarrow2x+1=-5\)
\(\Leftrightarrow2x=-6\)
\(\Rightarrow x=-3\)
b) \(\left(7-x\right)^2-\left(-11\right)=15\)
\(\Leftrightarrow\left(7-x\right)^2=4\)
\(\Leftrightarrow\orbr{\begin{cases}7-x=2\\7-x=-2\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=5\\x=9\end{cases}}\)
c) \(2020^x-2019=-2019\)
\(\Leftrightarrow2020^x=0\)
=> ko tồn tại x thỏa mãn PT
a) \(11-\left(15-21\right)=x-\left(25-9\right)\)
\(\Leftrightarrow11-15+21+25-9=x\)
\(\Leftrightarrow x=33\)
b) \(2-x=17-\left(-5\right)\)
\(\Leftrightarrow2-x=22\)
\(\Leftrightarrow x=-20\)
c) \(x-12=\left(-9\right)-15\)
\(\Leftrightarrow x-12=-24\)
\(\Leftrightarrow x=-12\)
d) \(9-25=\left(7-x\right)-\left(25+7\right)\)
\(\Leftrightarrow-16=7-x-25-7\)
\(\Leftrightarrow x=-9\)
a) 11-(15+21)=x-(25-9)
11-36=x-25+9
-25=x-(25+9)
-25=x-34
x=-25+34
x=9
Vậy x=9
b) 2-x=17-(-5)
2-x=22
x=2-22
x=-20
Vậy x=-20
c) x-12=(-9)-15
x-12=-24
x=-24+12
x=-12
Vậy x=-12
d) 9-25=(7-x)-(25+7)
16=7-x-32
48=7-x
x=-41
Vậy x=-41
a) \(x+\left(-81\right)-\left(11-81\right)=x-81-11+81=x-11\)
b) \(\left(-1-x+2\right)+1=\left(-1\right)-x+2+1=-x+2=2-x\)
c) \(15-\left(11-x\right)+\left(11-15\right)=15-11-x+11-15\)
\(=\left(15-15\right)+\left(11-11\right)+x=0+0+x=x\)
d) \(15-\left(15-x+202\right)=15-15+x-202=x-202\)
a)x-81-11+81=x-11
b)(-1-x+2)+1=-1-x+2+1=2-x
c)15-(11-x)+(11-15)=15-11+x+11-15=x
d)15-(15-x+202)+202=15-15+x-202+202=x