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-12x(x - 5) + 7x(3 - x) = 5
-12x2 + 60 + 21x - 7x2 = 5
-19x2 + 21x + 60 - 5 = 0
-19x2 + 21x + 55 = 0
\(\Delta=b^2-4ac=21^2-4.55.\left(-19\right)=441+4180=4621>0\)
vậy phtrinh có hai nghiệm phân biệt:
\(x_1=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-21+\sqrt{4621}}{2.\left(-19\right)}=\frac{-21+\sqrt{4621}}{-38}\)
\(x_2=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-21-\sqrt{4621}}{2.\left(-19\right)}=\frac{-21-\sqrt{4621}}{-38}\)
\(-12x\left(x-5\right)+7x\left(3-x\right)=5\)
\(-12x^2+60+21x-7x^2=5\)
\(-19x^2+60+21x=5\)
\(-19x^2+21x=5-60=-55\)
\(-19x^2+21x+55=0\)
\(a=-19;b=-21;c=55\)
\(=B^2-4ac\)
\(=21^2-4\left(-19\right).55\)
\(\Delta=4621\)
Giá trị delta cao hơn 0, vì vậy pt có hai nghiệm
\(x_1=\frac{-b-\sqrt{\Delta}}{2a};x_2=\frac{-b+\sqrt{\Delta}}{2a}\)
\(x_1=\frac{-b-\sqrt{\Delta}}{2a}=\frac{\left(-21\right)-\sqrt{4621}}{2.\left(-19\right)}=\frac{-21-\sqrt{4621}}{-38}\)
\(x_2=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-21+\sqrt{4621}}{2.\left(-19\right)}=\frac{-21+\sqrt{4621}}{-38}\)
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a: Ta có: \(7x+25=144\)
\(\Leftrightarrow7x=119\)
hay x=17
b: Ta có: \(33-12x=9\)
\(\Leftrightarrow12x=24\)
hay x=2
c: Ta có: \(128-3\left(x+4\right)=23\)
\(\Leftrightarrow3\left(x+4\right)=105\)
\(\Leftrightarrow x+4=35\)
hay x=31
d: Ta có: \(71+\left(726-3x\right)\cdot5=2246\)
\(\Leftrightarrow5\left(726-3x\right)=2175\)
\(\Leftrightarrow726-3x=435\)
\(\Leftrightarrow3x=291\)
hay x=97
e: Ta có: \(720:\left[41-\left(2x+5\right)\right]=40\)
\(\Leftrightarrow41-\left(2x+5\right)=18\)
\(\Leftrightarrow2x+5=23\)
\(\Leftrightarrow2x=18\)
hay x=9
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-12.(x-5)+7.(3-x)=5
=>-12x-(-60)+21-7x=5
=>-12x+60+21-7x=5
=>-12x-7x=5-21-60
=>(-12-7).x=-76
=>-19x=-76
=>x=(-76):(-19)
=>x=4
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( 7.x - 15 ) : 3 = 2
7.x - 15 = 6
7.x = 6 + 15
7.x = 21
x = 3
không biết vì chưa học
88 - 3 ( 7 + x ) = 64
3 ( 7 + x ) = 88 - 64
3 ( 7 + x ) = 24
7 + x = 8
x = 1
(7.x -15):3=2
7.x-15=2.3
7.x-15=6
7.x=6+15
7.x=21
x=21:7
x=3
12.(x+37)=504
x+37=504:12
x+37=42
x=42-37
x=5
88-3(7+x)=64
3(7+x)=88-64
3(7+x)=24
7+x=24:3
7+x=8
x=8-7
x=1
dấu . là nhân nhé
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a, 7x + 10x = 5x
17x = 5x
17x - 5x = 0
12x = 0
x =0
2;
a, 4x + 7x = 22
11x = 22
x = 2
b, 12x - 8x = 25
4x = 25
x = \(\dfrac{25}{4}\)
c, \(\dfrac{1}{2}\)x - \(\dfrac{1}{3}\)x = \(\dfrac{4}{5}\)
(\(\dfrac{1}{2}-\dfrac{1}{3}\))x = \(\dfrac{4}{5}\)
\(\dfrac{1}{6}\)x = \(\dfrac{4}{5}\)
x = \(\dfrac{4}{5}\) : \(\dfrac{1}{6}\)
x = \(\dfrac{24}{5}\)
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\(\Leftrightarrow21x-7x^2-12x^2+60x=0\Leftrightarrow-19x^2+81x=0\)
\(\Leftrightarrow x\left(-19x+81\right)=0\Leftrightarrow x=0;x=\dfrac{81}{19}\)