55 x 10
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\(x+2x+3x+...+10x=550\)
\(\Leftrightarrow (1+2+3+...+10)x=550\)
\(\Leftrightarrow 55x=550\)
\(\Leftrightarrow x=10\)
Đáp án \(A\)
Ta có: \(\left(x+2\right)\left(x-2\right)\left(x^2-10\right)=55\)
\(\Leftrightarrow\left(x^2-4\right)\left(x^2-10\right)=55\)
\(\Leftrightarrow x^4-10x^2-4x^2+40=55\)
\(\Leftrightarrow x^4-14x^2-15=0\)
Đặt \(t=x^2\left(t\ge0\right)\), ta có: \(t^2-14t-15=0\)\(\Leftrightarrow\left[{}\begin{matrix}t=15\\t=-1\left(loại\right)\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x=\sqrt{15}\\x=-\sqrt{15}\end{matrix}\right.\)
<=>\(\left(x^2-4\right)\left(x^2-10\right)=55\)
<=>\(x^4-14x^2+40=55\)
<=>\(x^4-14x^2-15=0\)
<=>\(\left(x^2-15\right)\left(x^2+1\right)=0\)
<=>\(x^2-15=0\)(cái kia lun lớn hơn 0)
<=>\(x^2=15\)
<=>\(x=\pm\sqrt{15}\)
\(x⋮10,x⋮20\) tức x chia hết cho 30
55 < x < 65
= > x = 60
\(\dfrac{x-9}{55}+\dfrac{x-10}{66}=\dfrac{x-11}{77}+\dfrac{x-12}{88}\\ \Leftrightarrow\left(\dfrac{x-9}{55}+\dfrac{1}{11}\right)+\left(\dfrac{x-10}{66}+\dfrac{1}{11}\right)-\left(\dfrac{x-11}{77}+\dfrac{1}{11}\right)-\left(\dfrac{x-12}{88}+\dfrac{1}{11}\right)=0\)
\(\Leftrightarrow\left(\dfrac{x-9}{55}+\dfrac{5}{55}\right)+\left(\dfrac{x-10}{66}+\dfrac{6}{66}\right)-\left(\dfrac{x-11}{77}+\dfrac{7}{77}\right)-\left(\dfrac{x-12}{88}+\dfrac{8}{88}\right)=0\)
\(\Leftrightarrow\dfrac{x-4}{55}+\dfrac{x-4}{66}-\dfrac{x-4}{77}-\dfrac{x-4}{88}=0\)
\(\Leftrightarrow\left(x-4\right)\left(\dfrac{1}{55}+\dfrac{1}{66}-\dfrac{1}{77}-\dfrac{1}{88}\right)=0\\ \Leftrightarrow x=4\left(vì.\dfrac{1}{55}+\dfrac{1}{66}-\dfrac{1}{77}-\dfrac{1}{88}\ne0\right)\)
d,155-10(x+1)=55
10(x+1) = 155 - 55
10(x+1) = 100
x+1 = 100 : 10
x+1 = 10
x = 10 - 1 =9
e,6(x+\(2^3\))+40=100
6(x+\(2^3\)) = 100 - 40
6(x+\(2^3\)) = 60
(x+\(2^3\)) = 60 : 6
(x+\(2^3\)) = 10
x = 10 - \(2^3\)
x = 10 - 8 = 2
f,\(2^2\)(x+\(3^2\))-5=55
\(2^2\)(x+\(3^2\)) = 55 + 5
\(2^2\)(x+\(3^2\)) = 60
(x+\(3^2\)) = 60 : \(2^2\)
(x+\(3^2\)) = 60 : 4
(x+\(3^2\)) = 15
x + 9 = 15
x = 15-9=6.
Hok tốt !
d) \(155-10\left(x+1\right)=55\)
\(\Rightarrow10\left(x+1\right)=155-55\)
\(\Rightarrow10\left(x+1\right)=100\)
\(\Rightarrow x+1=100:10\)
\(\Rightarrow x+1=10\)
\(\Rightarrow x=10-1\)
\(\Rightarrow x=9\)
Vậy x = 9
e) \(6\left(x+2^3\right)+40=100\)
\(\Rightarrow6\left(x+2^3\right)=100-40\)
\(\Rightarrow6\left(x+2^3\right)=60\)
\(\Rightarrow x+2^3=60:6\)
\(\Rightarrow x+2^3=10\)
\(\Rightarrow x+8=10\)
\(\Rightarrow x=10-8\)
\(\Rightarrow x=2\)
Vậy x = 2
f) \(2^2\left(x+3^2\right)-5=55\)
\(\Rightarrow2^2\left(x+3^2\right)=55+5\)
\(\Rightarrow2^2\left(x+3^2\right)=60\)
\(\Rightarrow4\left(x+9\right)=60\)
\(\Rightarrow x+9=60:4\)
\(\Rightarrow x+9=15\)
\(\Rightarrow x=15-9\)
\(\Rightarrow x=6\)
Vậy x = 6
555 x 5510 = 5515
666612 x 666610 = 666622
510 x 51 = 511
221 x 2210 = 2211
101 x 102 = 1012
555x5510=5515
666612x666610=666622
510x51=511
221x 2210=2211
101x102=103
155 - 10 .( x+1 ) = 55
155 - 55 = 10 ( x + 1 )
100 = 10 ( x + 1 )
100 : 10 = x+ 1
10 = x + 1
10 - 1 = x
9 = x
Vậy x = 9
55 x 10 = 550
k nhé
550 la ket qua