tính hợp lý:2^12*243-4^6*9^2/(2^2*3)^6+8^4*3^5
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em lớp 6
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12-12+11+10-9+8-7+6-4+3+2-1
=(12-12)+[11-(7+4)]+[10-(9+1)]+(8+2)+(6+3)
=0+0+0+10+9
=19
12-12+11+10-9+8-7+6-4+3+2-1
=[12-12]+[11-1]+10+[8+2]-[7+3]+[9+6+4]
=0+10+10+10-10+19
=19
Ta có : A = \(\frac{\left(2^2.3\right)^6+8^4.3^5}{2^{12}.3^5-4^6.9^2}\)
= \(\frac{\left(2^2\right)^6.3^6+\left(2^3\right)^4.3^5}{2^{12}.3^5-\left(2^2\right)^6.\left(3^2\right)^2}\)
= \(\frac{2^{12}.3^6+2^{12}.3^5}{2^{12}.3^5-2^{12}.3^4}\)
= \(\frac{2^{12}.\left(3^6+3^5\right)}{2^{12}.\left(3^5-3^4\right)}\)
= \(\frac{3^6+3^5}{3^5-3^4}\)
= \(6\)
\(A=\frac{\left(2^2.3\right)^6+8^4.3^5}{2^{12}.3^5-4^6.9^2}\)
\(A=\frac{2^{12}.3^6+\left(2^3\right)^4.3^5}{2^{12}.3^5-\left(2^2\right)^6.\left(3^2\right)^2}\)
\(A=\frac{2^{12}.3^6+2^{12}.3^5}{2^{12}.3^5-2^{12}.3^4}\)
\(A=\frac{2^{12}.\left(3^6+3^5\right)}{2^{12}.\left(3^5-3^4\right)}\)
\(\Rightarrow A=\frac{3^5.\left(3+1\right)}{3^4.\left(3-1\right)}=\frac{3^5.4}{3^4.2}=\frac{3.3^4.2.2}{3^4.2}=\frac{3.2}{1}=6\)
a.
\(A=5.\left(2^2\right)^{15}.\left(3^2\right)^9-2^2.3^{20}.\left(2^3\right)^9=5.2^{30}.3^{18}-2^2.3^{20}.2^{27}\)
\(=5.2^{30}.3^{18}-3^{20}.2^{29}=2^{29}.3^{18}.\left(5.2-3^2\right)=2^{29}.3^{18}\)
\(B=5.2^9.\left(2.3\right)^{19}-7.2^{29}.\left(3^3\right)^6=5.2^9.2^{19}.3^{19}-7.2^{29}.3^{18}=5.2^{28}.3^{19}-7.2^{29}.3^{18}\)
\(=2^{28}.3^{18}.\left(5.3-7.2\right)=2^{28}.3^{18}\)
=> \(A:B=\left(2^{29}.3^{18}\right):\left(2^{28}.3^{18}\right)=\frac{\left(2^{29}.3^{18}\right)}{\left(2^{28}.3^{18}\right)}=2\)
b. kiểm tra lại đề bài nhé
`a, 4/9 + 2/5 + 5/9= (4/9 +5/9) + 2/5= 1 + 2/5= 5/5 + 2/5= 7/5`
`b, 6/13 + 5/8 + 7/13=(6/13 + 7/13) + 5/8=1+5/8= 8/8 + 5/8= 13/8`
`c, 5/11 + 6/25 + 66/121 = ( 5/11 + 66/121 ) + 6/25=1 + 6/25 = 25/25 + 6/25 = 31/25`
`d, 1/2 + 1/3 + 1/4 + 1/6 + 1/12 + 1/24= (1/2 + 1/4) +(1/3 + 1/6) + (1/12 + 1/24)= 3/4 + 1/2 + 1/8= 6/8 + 4/8 + 1/8= 11/8`
`@ yl`
\(\frac{3^2.9^3.25^2.12^6}{3^{15}.5^4.6^3.4^2}=\frac{3^2.3^{2.3}.5^{2.2}.3^6.4^6}{3^{15}.5^4.2^3.3^3.2^{2.2}}=\frac{3^2.3^6.3^6.5^4.2^{2.6}}{3^{15}.3^3.5^4.2^3.2^4}=\frac{3^{14}.2^{12}.5^4}{3^{18}.5^4.2^7}=\frac{2^5}{3^4}=\frac{32}{81}\)
\(\frac{2^{12}.243-4^6.9^2}{\left(2^2.3\right)^6+8^4.3^5}\)
\(=\frac{2^{12}.3^5-2^{12}.3^4}{2^{12}.3^6+2^{12}.3^5}\)
\(=\frac{2^{12}.3^4.\left(3-1\right)}{2^{12}.3^5.\left(3-1\right)}\)
\(=\frac{1}{3}\)
HT