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a) Bạn Nguyễn Lê Phước Thịnh giải rồi nha bạn :)
b) (-9-x+2)+9
=-9-x+2+9
=-9+(-x)+2+9
=(-x)+(-9+2+9)
=(-x)+2
c) 66-(12-x)+(12-66)
=66-12+x+12-66
=x
d) 15-(15-x+93)+93
=15-15+x-93+93
=x
Lời giải:
\(P=\frac{2^{19}.27^3+15.4^9.9^4}{6^9.2^{10}+12^{10}}\\ =\frac{2^{19}.3^9+3.5.2^{18}.3^8}{2^9.3^9.2^{10}+2^{20}.3^{10}}\\ =\frac{2^{19}.3^9+2^{18}.3^9.5}{2^{19}.3^9+2^{20}.3^{10}}\\ =\frac{2^{18}.3^9(2+5)}{2^{19}3^9(1+2.3)}\\ =\frac{1}{2}\)
12/15 = 4/5 15/10 = 3/2
14/21 = 2/3 70/20 = 7/2
18/12 = 3/2 55/66 = 5/6
( 4/5 - 2/3 - 3/2 ) : ( 3/2 - 7/2 - 5/6 ) = -41/30 : -17/6
= 41/85
\(\frac{15x8+15x4}{12x3}\)
\(=\frac{15x\left(8+4\right)}{12x3}\)
\(=\frac{15x12}{12x3}=\frac{15}{3}=5\)
\(4^{18}.8^{15}=\left(2^2\right)^{18}.\left(2^3\right)^{15}\)
\(=2^{36}.2^{45}\)
\(=2^{81}\)
\(4^{15}.5^{30}=\left(2^2\right)^{15}.5^{30}\)
\(=2^{30}.5^{30}\)
\(=\left(2.5\right)^{30}\)
\(=10^{30}\)
\(\frac{3.72^2.54^2}{108^4}=\frac{3.\left(3^2.2^3\right)^2.\left(3^3.2\right)^2}{\left(3^3.2^2\right)^4}\)
\(=\frac{3.3^4.2^6.3^6.2^2}{3^{12}.2^8}\)
\(=\frac{3^{11}.2^8}{3^{12}.2^8}\)
\(=\frac{1}{3}\)
\(\frac{2^{15}\times9^4}{6^6\times8^3}=\frac{2^{15}\times\left(3^2\right)^4}{3^6\times2^6\times\left(2^3\right)^3}=\frac{2^{15}\times3^{18}}{3^6\times2^{15}}=\frac{3^8}{3^6}=3^2=9\)
\(\frac{2^{15}.9^4}{6^6.8^3}=\frac{2^{15}.\left(3^2\right)^4}{\left(3.2\right)^6.\left(2^3\right)^3}=\frac{2^{15}.3^8}{3^6.2^6.2^9}=\frac{2^{15}.3^8}{3^6.2^{15}}=3^2=9\)