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A=1+3^2+3^4+...+3^100
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1/2* x+2/3=9/2
1/2 * x = 9/2 - 2/3
1/2 * x= 23/6
x= 23/6 : 1/2
x= 23/6 x 2= 23/3
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1/2*x-1/3=2/3
1/2*x = 2/3 + 1/3
1/2 * x= 1
x= 1: 1/2
x= 2
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1/4+3/4:x=3
3/4 : x = 3 - 1/4
3/4 : x= 11/4
x= 11/4 : 3/4
x= 11/3
\(\dfrac{1}{2}\)\(\times\)\(x\) + \(\dfrac{2}{3}\) = \(\dfrac{9}{2}\)
\(\dfrac{1}{2}\)\(\times\)\(x\) = \(\dfrac{9}{2}\) - \(\dfrac{2}{3}\)
\(\dfrac{1}{2}\)\(\times\)\(x\) = \(\dfrac{23}{6}\)
\(x\) = \(\dfrac{23}{6}\):\(\dfrac{1}{2}\)
\(x\) = \(\dfrac{23}{3}\)
\(\dfrac{1}{2}\)\(\times\)\(x\) - \(\dfrac{1}{3}\) = \(\dfrac{2}{3}\)
\(\dfrac{1}{2}\)\(\times\)\(x\) = \(\dfrac{2}{3}\) + \(\dfrac{1}{3}\)
\(\dfrac{1}{2}\times\)\(x\) = 1
\(x\) = 1 : \(\dfrac{1}{2}\)
\(x\) = 2
\(\dfrac{1}{4}\) + \(\dfrac{3}{4}\): \(x\) = 3
\(\dfrac{3}{4}\): \(x\) = 3 - \(\dfrac{1}{4}\)
\(\dfrac{3}{4}\):\(x\) = \(\dfrac{11}{4}\)
\(x\) = \(\dfrac{3}{4}\): \(\dfrac{11}{4}\)
\(x\) = \(\dfrac{3}{11}\)
\(\frac{1}{2}.\frac{2}{3}.\)\(...\frac{99}{100}=\frac{1.2.....99}{2.3.....100}=\frac{1.\left(2.....99\right)}{\left(2.3.....99\right).100}=\frac{1}{100}\)
hình như đề sai vì x + (-2/3) không thể bằng x + 1/4 đúng k nhỉ :)
\(=\dfrac{3}{2}-\dfrac{2}{21}-\dfrac{7}{12}+\left[\dfrac{15}{21}-\dfrac{1}{3}+\dfrac{5}{4}-\dfrac{2}{7}-\dfrac{1}{3}\right]\)
=11/12-2/21+5/7-2/3+5/4-2/7
=11/12-2/3+5/4-2/21+3/7
=11/12-8/12+15/12-2/21+9/21
=18/12+7/21
=3/2+1/3
=9/6+2/6=11/6
\(B=\dfrac{3}{2}-\dfrac{2}{21}-\left\{\dfrac{7}{12}-\left[\dfrac{15}{21}-\left(\dfrac{1}{3}-\dfrac{5}{4}\right)-\left(\dfrac{2}{7}+\dfrac{1}{3}\right)\right]\right\}\)
\(B=\dfrac{3}{2}-\dfrac{2}{21}-\left\{\dfrac{7}{12}-\left[\dfrac{15}{21}-\left(-\dfrac{11}{12}\right)-\dfrac{13}{21}\right]\right\}\)
\(B=\dfrac{3}{2}-\dfrac{2}{21}-\left\{\dfrac{7}{12}-\dfrac{85}{84}\right\}\)
\(B=\dfrac{3}{2}-\dfrac{2}{21}-\left(-\dfrac{3}{7}\right)\)
\(B=\dfrac{11}{6}\)
a)
(1/3-1/5)x1/4 = 1/3x1/4-1/5x1/4=1/12-1/20=1/30
(1/3-1/5)x1/4 = 2/15x1/4=1/30
b)
2/5 x 3/7 + 2/5 x 4/7= 6/35 + 8/35 = 14/35 = 2/5
2/5 x 3/7 + 2/5 x 4/7= (3/7+4/7) x 2/5 = 1 x 2/5 = 2/5
Tham khảo tại link này nha : dog
[ Toán 7] Tính A: $A=1+3+3^2+....+3^{100} $ | HOCMAI Forum - Cộng đồng học sinh Việt Nam
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