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\(9^x:3^x=3^7\)
\(\Rightarrow9:3^x=3^7\)
\(\Rightarrow3^x=3^7\)
\(\Rightarrow x=7\)
Bài 2:
a: \(=7^4\left(7^2+7-1\right)=7^4\cdot55⋮55\)
b: \(5A=5+5^2+...+5^{51}\)
\(\Leftrightarrow4A=5^{51}-1\)
hay \(A=\dfrac{5^{51}-1}{4}\)
Bài 3:
\(S=\left(1^2+2^3+3^3+...+10^2\right)\cdot2=385\cdot2=770\)
Ta thấy A gấp 12+22+....+102 4 lần nên Tổng A gấp 4 lần nó
=> A=385.4=1540
tại sao A lại gấp 12+22+.......+102 4 lần vậy,bạn giải thích rõ đc ko?
a) A=\(\frac{2^{13}.3^5-4^6.9^2}{\left(2^2.3\right)^6+8^4.3^5}-\frac{5^{10}.7^5-25^3.49^2}{\left(125.7\right)^3+5^9.14^3}\) =\(\frac{2^{13}.3^5-\left(2^2\right)^6.\left(3^2\right)^2}{\left(2^2\right)^6.3^6+\left(2^3\right)^4.3^5}-\frac{5^{10}.7^5-\left(5^2\right)^3.\left(7^2\right)^2}{\left(5^3\right)^3.7^3+5^9.\left(2.7\right)^3}\) =\(\frac{2^{13}.3^5-2^{12}.3^4}{2^{12}.3^6+2^{12}.3^5}-\frac{5^{10}.7^5-5^6.7^4}{5^9.7^3+5^9.2^3.7^3}\) =\(\frac{2^{12}.3^4.\left(2.3-1\right)}{2^{12}.3^5.\left(6+1\right)}-\frac{5^6.7^4.\left(5^4.7-1\right)}{2^3.5^9.7^3\left(1+1.2^3\right)}\) =\(\frac{2^{12}.3^4.5}{2^{12}.3^5.7}-\frac{5^6.7^4.4374}{3^3.5^9.7^3.9}\) =\(\frac{5}{3.7}-\frac{7.4374}{3^3.5^3.3^2}\) =\(\frac{5}{21}-\frac{7.4374}{3^6.5^3}\) =\(\frac{5}{21}-\frac{7.4374}{729.125}\) =\(\frac{5}{21}-\frac{42}{125}\) =\(\frac{-257}{2625}\) b)S=\(2^2+4^2+....+20^2\) =\(\left(1.2\right)^2+\left(2.2\right)^2+....+\left(10.2\right)^2\) =\(2^2.\left(2^2+4^2+....+10^2\right)\) =\(2^2.385\) =4.385 =\(1540\)
a) 7x+2 + 2.7x-1 = 345
7x-1 . 73 + 2.7x-1 = 345
7x-1.(343+2) = 345
7x-1. 345=345
=> 7x-1=1
=> 7x-1=70
=> x-1 =0
x=1
b)\(\frac{1}{2}\).2x + 2x+2= 28+25
\(\frac{1}{2}\).2x + 2x . 22 = 288
2x . ( \(\frac{1}{2}\)+ 4)= 288
2x . \(\frac{9}{2}\)=288
=>2x=64
2x= 26
=>x=6
c)2.3x +3x-1 = 7.( 32+2.62)
2.3x-1.31 + 3x-1 = 567
3x-1.(6+1)=567
3x-1.7=567
=>3x-1= 81
3x-1=34
=>x-1=4
x=5