tính giá trị biểu thức : 1+2.6+3.6^2+.......+100.6^99
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Trả lời :
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Ta có:
\(A=1+2.6+3.6^2+4.6^3+...+100.6^{99}\)
=> \(6A=6+2.6^2+3.6^3+....+99.6^{99}+100.6^{100}\)
=> A - 6A = \(1+6+6^2+6^3+...+6^{99}-100.6^{100}\)
=> \(-5A=1+6+6^2+...+6^{99}-100.6^{100}\)
Đặt: \(B=1+6+6^2+...+6^{99}\)
=> \(6B=6+6^2+6^3+...+6^{100}\)
=> 6 B - B = \(6^{100}-1\)
=> B = \(\frac{6^{100}-1}{5}\)
=> \(-5A=\frac{6^{100}-1}{5}-100.6^{100}\)
=> \(A=\frac{499.6^{100}+1}{25}\)
\(A=\dfrac{4^5.9^4-2.6^9}{2^{10}.3^8+6^8.20}\)
\(=\dfrac{2^{10}.3^8-2.2^9.3^9}{2^{10}.3^8+2^8.3^8.2^2.5}\)
\(=\dfrac{2^{10}.3^8-2^{10}.3^9}{2^{10}.3^8+2^{10}.3^8.5}\)
\(=\dfrac{2^{10}.3^8\left(1-3\right)}{2^{10}.3^8\left(1+5\right)}\)
\(=-\dfrac{2}{6}=-\dfrac{1}{3}\)
( 4^5.9^4+2.6^9) : (2^10.3^8-6^8.2) = \(\frac{4^5.9^4+2.6^9}{2^{10}.3^8-6^8.2}=\frac{\left(2^2\right)^5.\left(3^2\right)^4+2.6^9}{2^{10}.3^8-6^8.2}\)
= \(\frac{2^{10}.3^8+2.6^9}{2^{10}.3^8-6^8.2}=\frac{2\left(6^8.8\right)}{2.6^8}=\frac{6^8.8}{6^8}=8\)
(0.6)^5/(0.2)^6
= [(0.2)^5. 3^5]/(0.2)^6
= 3^5/0.2
=243/0.2
= 1215
6^3+3.6^2+3^3/-13
= 2^3.3^3+3.2^2.3^2+3^3/-13
=3^3(2^3+2^2+1)/-13
=3^3.13/-13
=-27
\(\frac{6^3+3\cdot6^2+3^3}{-13}=\frac{\left(3\cdot2\right)^3+3\cdot\left(3\cdot2\right)^2+3^3}{-13}=\frac{3^3\cdot2^3+3\cdot3^2\cdot2^2+3^3}{-13}=\frac{3^3\cdot\left(2^3+2^2+1\right)}{-13}=\frac{27\cdot13}{-13}=-27\)