Giải giúp mik với bn iu

Đáp án:

 `\textb\color{#FF8C00}t\color{#FFA000}r\color{#FFB400}i\color{#FFC800}b\color{#FFDC00}u\color{#FFE000}i\color{#FFE400}6\color{#FFEA00}1\color{#FFF000}2\color{#FFF500}2`

`color(blue)text(Toán học`

Giải thích các bước giải:

`A=1/(1*2)+1/(2*3)+...+1/(19*20)`

`A=1-1/2+1/2-1/3+...+1/19-1/20`

`A=1-1/20`

`A=19/20.`

Vậy `bb(A=19/20.`

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`B=4/(1*3)+4/(3*5)+...+4/(97*99)`

`B/2=2/(1*3)+2/(3*5)+...+2/(97*99)`

`B/2=1-1/3+1/3-1/5+...+1/97-1/99`

`B/2=1-1/99`

`B/2=98/99`

`B=98/99-:1/2`

`B=196/99.`

Vậy `bb(B=196/99.`

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`C=3/(1*4)+3/(4*7)+...+3/(91*94)`

`C=1-1/4+1/4-1/7+...+1/91-1/94`

`C=1-1/94`

`C=93/94.`

Vậy `bb(C=93/94.`

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`D=(1-1/2)*(1-1/3)*...*(1-1/100)`

`D=1/2*2/3*...*99/100`

`D=(1*2*...*99)/(2*3*...*100)`

`D=1/100.`

Vậy `bb(D=1/100.`

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`E=(1+1/2)*(1+1/3)*...*(1+1/100)`

`E=3/2*4/3*...*101/100`

`E=(3*4*...*101)/(2*3*...*100)`

`E=101/2.`

Vậy `bb(E=101/2.`