Đáp án:
Giải thích các bước giải:
`A=3+3^2+3^3+...+3^30`
`=>A/3=(3+3^2+3^3+...+3^30)/3`
`=>A/3=1+3+3^2+...+3^29`
`=>A-A/3=(3+3^2+3^3+...+3^30)-(1+3+3^2+...+3^29)`
`=>(2A)/3=3^30-1`
`=>2A=3(3^30-1)`
`=>2A=3^31-3`
`=>A=(3^31-3)/2`
`B=1/7+(1/7)^2+(1/7)^3+...+(1/7)^70`
`=>7B=1+1/7+(1/7)^2+...+(1/7)^69)`
`=>7B-B=(1+1/7+(1/7)^2+...+(1/7)^69)-(1/7+(1/7)^2+(1/7)^3+...+(1/7)^70)`
`=>6B=1-(1/7)^70`
`=>`$B=\dfrac{1-\left(\dfrac{1}{7}\right)^{70}}{6}$
`C=(4^2. 5^4. 6^3)/(10^3. 3^2 .5)`
`=>C=(2^(2^2). 5^3. (2.3)^3)/((2.5)^3. 3^2)`
`=>C=(2^4. 5^3. 2^3. 3^3)/(2^3 .5^3. 3^2`
`=>C=2. 2^3 .3`
`=>C=48`
`D=(27^2. 25^4. 16^3)/(8^6. 5^8. 9^8)`
`=>D=((3^3)^2. (5^2)^4.(2^4)^3)/((2^3)^6. 5^8. (3^2)^2`
`=>D=(3^6. 5^8. 2^12)/(2^18. 5^8. 3^4`
`=>D=3^2. 2^(-6)`
