Tính nhanh :
A ) 10 315 x 36 - 17 205 x 18 + 18
B ) 1/7 x 3/5 + 1/7 x 2/5
Giúp với ạ :(
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\(\left(2x-1\right)\left(3x+1\right)+\left(3x+4\right)\left(3x-2\right)=5\)
=>\(6x^2+2x-3x-1+9x^2-6x+12x-8=5\)
=>\(15x^2+5x-9-5=0\)
=>\(15x^2+5x-14=0\)
\(\Delta=5^2-4\cdot15\cdot\left(-14\right)=25+60\cdot14=25+840=865>0\)
Do đó: Phương trình có hai nghiệm phân biệt là:
\(\left[{}\begin{matrix}x=\dfrac{-5-\sqrt{865}}{2\cdot15}=\dfrac{-5-\sqrt{865}}{30}\\x=\dfrac{-5+\sqrt{865}}{30}\end{matrix}\right.\)
\(12,3-2\left(x+1,3\right)=5,7\)
\(2\left(x+1,3\right)=12,3-5,7\)
\(2\left(x+1,3\right)=6,6\)
\(x+1,3=6,6:2\)
\(x+1,3=3,3\)
\(x=3,3-1,3\)
\(x=2\)
23,4 + \(x\) : 0,2 = 25,3
\(x:\) 0,2 = 25,3 - 23,4
\(x\) : 0,2 = 1,9
\(x\) = 1,9 x 0,2
\(x\) =
Vậy \(x=0,38\)
a; - \(\dfrac{3}{5}\) + \(\dfrac{7}{5}\) = \(\dfrac{-3+7}{5}\) = \(\dfrac{4}{5}\)
b; \(\dfrac{3}{5}\) - \(\dfrac{-9}{5}\) = \(\dfrac{3-\left(-9\right)}{5}\) = \(\dfrac{3+9}{5}\) = \(\dfrac{12}{5}\)
c; \(\dfrac{23}{-11}\) - \(\dfrac{-3}{11}\) = \(\dfrac{-23}{11}\) + \(\dfrac{3}{11}\) = \(\dfrac{-20}{11}\)
d; -2\(\dfrac{1}{3}\) - 1\(\dfrac{3}{4}\)
= \(\dfrac{-7}{3}\) - \(\dfrac{7}{4}\)
= \(\dfrac{-28}{12}\) - \(\dfrac{21}{12}\)
= \(\dfrac{-49}{12}\)
e; (- \(\dfrac{1}{3}\))(-\(\dfrac{9}{13}\))
= \(\dfrac{3}{13}\)
f; 1\(\dfrac{1}{2}\) x (- \(\dfrac{10}{9}\))
= \(\dfrac{3}{2}\) x (- \(\dfrac{10}{9}\))
= - \(\dfrac{5}{3}\)
\(64=8^2;100=10^2\)
\(121=11^2\)
\(169=13^2\)
\(196=14^2\)
\(289=17^2\)
`a, 10315` $\times $ `36 - 17025` $\times $ `18 + 18`
`= 10315` $\times $ `2` $\times $ `18 -17025` $\times $ `18 + 18`
`= 20630` $\times $ `18 - 17025` $\times $ `18+18`
`= 18` $\times $ `(20630-17025+1)`
`= 18` $\times $ `3606`
`=64908`
`b, 1/7` $\times $ `3/5 + 1/7` $\times $ `2/5`
`= 1/7` $\times $ `(3/5+2/5)`
`= 1/7` $\times $ `1`
`= 1/7`