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\(\left(5x^2-2x+1\right)\left(2x^2-3x\right)=10x^4-15x^3-4x^3+6x^2+2x^2-3x\)
\(=10x^4-19x^3+8x^2-3x\)
\(=\dfrac{1}{11}-\dfrac{1}{11}+\dfrac{1}{41152}=\dfrac{1}{41152}\)
\(\dfrac{3}{5}+\dfrac{13}{25}-\dfrac{5}{9}-\dfrac{3}{7}\)
\(=\dfrac{15}{25}+\dfrac{13}{25}-\dfrac{35}{63}-\dfrac{27}{63}\)
\(=\dfrac{28}{25}-\dfrac{62}{63}=\dfrac{214}{1575}\)
Bài 3:
a)3.52-16:22=71
b)15.141+59.15=15(141+59)=3000
c)23.17-23.14=23(17-14)=8.3=24
(câu b hình như thiếu dấu "+"?)
a. `17.85+15.17-120`
`=17 . (85+15)-120`
`=17 . 100-120`
`=1700-120`
`=1580`
b. `5.7^2 - 24 : 2^3`
`=5. 49 - 24: 8`
`=245-3`
`=242`
c. `3^3 .22 -27.19`
`=27.22 - 27.19`
`=27 . (22-19)`
`=27.3=81`
a: \(3200:40\cdot2=160\)
b: \(3920:28:2=70\)
c: \(\left(3^4\cdot5^7-9^2\cdot21\right):3^5=3^2\cdot5^7-7=703118\)
Dạng tổng quát: \(\dfrac{a+b}{ab}=\dfrac{1}{a}+\dfrac{1}{b}\)
Áp dụng:
\(A=\dfrac{3}{1.2}-\dfrac{5}{2.3}+\dfrac{7}{3.4}-...+\dfrac{15}{7.8}-\dfrac{17}{8.9}\)
\(=\left(1+\dfrac{1}{2}\right)-\left(\dfrac{1}{2}+\dfrac{1}{3}\right)+\left(\dfrac{1}{3}+\dfrac{1}{4}\right)-...+\left(\dfrac{1}{7}+\dfrac{1}{8}\right)-\left(\dfrac{1}{8}+\dfrac{1}{9}\right)\)
\(=1+\dfrac{1}{2}-\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}+\dfrac{1}{4}-...+\dfrac{1}{7}+\dfrac{1}{8}-\dfrac{1}{8}-\dfrac{1}{9}\)
\(1-\dfrac{1}{9}=\dfrac{8}{9}\)
lộn đề bài r: \(3.\dfrac{1}{1.2}-5.\dfrac{1}{2.3}+7.\dfrac{1}{3.4}-...+15.\dfrac{1}{7.8}-17.\dfrac{1}{8.9}\)
\(a,\left\{\left[\left(37+13\right):5\right]-45:5\right\}.7\)
\(=\left\{\left[50:5\right]-45:5\right\}.7\)
\(=\left\{10-45:5\right\}.7\)
\(=\left\{10-9\right\}.7\)
\(=1.7=7\)
a: \(\left(-35,3\right)\cdot4,1=-\left(35,3\cdot4,1\right)=-144,73\)
b: \(2,9\cdot\left(-5,4\right)=-2,9\cdot5,4=-15,66\)
c: \(\left(-3,25\right)\cdot\left(-0,21\right)=3,25\cdot0,21=\frac{273}{400}\)
d: \(\left(-8,058\right):3,4=-8,058:3,4=-2,37\)
e: \(\left(-4,725\right):\left(-1,5\right)=4,725:1,5=3,15\)
f: \(82,28:\left(-4,4\right)=-82,28:4,4=-18,7\)
a) -144,73
b) -15,66
c) 0,6825
d) -2,37
e) 3,15
f) -18,7