Tính bằng cách hợp lí :
2 x a + 3 x a + a = 2046
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\(a,\dfrac{3}{2}\times\dfrac{4}{5}\times\dfrac{2}{3}\times\dfrac{15}{4}\\ =\dfrac{3\times4\times2\times15}{2\times5\times3\times4}\\ =\dfrac{3\times4\times2\times5\times3}{2\times5\times3\times4}\\ =3\)
\(b,\dfrac{6}{7}\times\dfrac{5}{8}\times\dfrac{7}{3}\times\dfrac{7}{6}\times\dfrac{8}{5}\\ =\dfrac{6\times5\times7\times7\times8}{7\times8\times3\times6\times5}\\ =\dfrac{7}{3}\)
a) \(\dfrac{3}{2}\times\dfrac{4}{5}\times\dfrac{2}{3}\times\dfrac{15}{4}\)
\(=\left(\dfrac{3}{2}\times\dfrac{2}{3}\right)\times\left(\dfrac{4}{5}\times\dfrac{15}{4}\right)\)
\(=1\times3\)
\(=3\)
b) \(\dfrac{6}{7}\times\dfrac{5}{8}\times\dfrac{7}{3}\times\dfrac{7}{6}\times\dfrac{8}{5}\)
\(=\left(\dfrac{6}{7}\times\dfrac{7}{6}\right)\times\left(\dfrac{5}{8}\times\dfrac{8}{5}\right)\times\dfrac{7}{3}\)
\(=1\times1\times\dfrac{7}{3}\)
\(=\dfrac{7}{3}\)
Chúc bạn học tốt
a: A=(-x)^3+3*(-x)^2*2+3*(-x)*2^2+2^3=(-x+2)^3
=(28+2)^3=30^3=27000
b: \(C=\left(x+2y-2\right)^3=\left(20+2\cdot9-2\right)^3\)
=36^3
c: 11^3-1
=(11-1)(11^2+11+1)
=10*(121+12)
=1330
d: x^3-y^3=(x-y)^3+3xy(x-y)
=6^3+3*6*9
=216+162
=378
a. ( 4 x 25 ) x (5 x 9)
= 100 x 45
= 4500
b. (2008 x4) - ( 2008 x 4)
= 0
a) \(\frac{3}{5}+\frac{6}{11}+\frac{7}{13}+\frac{2}{5}+\frac{16}{11}+\frac{19}{13}\)
\(=\left(\frac{3}{5}+\frac{2}{5}\right)+\left(\frac{6}{11}+\frac{16}{11}\right)+\left(\frac{7}{13}+\frac{19}{13}\right)\)
\(=1+2+2=5\)
b) \(\frac{1995}{1997}x\frac{1990}{1993}x\frac{1997}{1994}x\frac{1993}{1995}x\frac{997}{995}=\frac{1995x1990x1997x1993x997}{1997x1993x1994x1995x995}=\frac{1990x997}{1994x995}=\frac{995x2x997}{997x2x995}=1\)
a) =(3/5+2/5)+(6/11+16/11)+(19/13+7/13)
=5/5+22/11+26/13
=1+2+3
=6
2 x a + 3 x a + a =2046
a x (2 +3 +1)= 2046
a x 6 =2046
a = 2046 : 6 = 341
2 x a + 3 x a + a = 2046 3 x a = 2043 a = 2043 : 3 a = 681