Question

[Nguyễn Đức Hùng]

 ai làm hộ mình phần 7 và 9 với mình đang cần gấp

Answer 1

[Akai Haruma]

7.

$(3\times x-1)\times (\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16})=\frac{15}{13}$

$(3\times x-1)\times \frac{8+4+2+1}{16}=\frac{15}{13}$

$(3\times x-1)\times \frac{15}{16}=\frac{15}{13}$

$3\times x-1=\frac{15}{13}: \frac{15}{16}=\frac{16}{13}$

$3\times x=\frac{16}{13}+1=\frac{29}{13}$

$x=\frac{29}{13}:3=\frac{29}{39}$

Answer 2

[Akai Haruma]

9.

$x+\frac{1}{1\times 2}+\frac{1}{2\times 3}+....+\frac{1}{99\times 100}=\frac{101}{100}$

$x+\frac{2-1}{1\times 2}+\frac{3-2}{2\times 3}+....+\frac{100-99}{99\times 100}=\frac{101}{100}$

$x+1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+....+\frac{1}{99}-\frac{1}{100}=\frac{101}{100}$

$x+1-\frac{1}{100}=\frac{101}{100}$

$x=\frac{101}{100}+\frac{1}{100}-1=\frac{1}{50}$