đề: Cho B = $frac{1}{2}$ + ($frac{1}{2}$)mũ 2 + ( $frac{1}{2}$ ) mũ 3 +…..+ ( $frac{1}{2}$ )mũ 99 Chứng minh rằng B<1 18/07/2021 Bởi Vivian đề: Cho B = $frac{1}{2}$ + ($frac{1}{2}$)mũ 2 + ( $frac{1}{2}$ ) mũ 3 +…..+ ( $frac{1}{2}$ )mũ 99 Chứng minh rằng B<1
$2B=1+\dfrac{1}{2}+(\dfrac{1}{2})^2+…+(\dfrac{1}{2})^{98}$ $2B-B=[1+\dfrac{1}{2}+(\dfrac{1}{2})^2+…+(\dfrac{1}{2})^{98}]-[\dfrac{1}{2}+(\dfrac{1}{2})^2+…(\dfrac{1}{2})^{99}]$ $B=1-(\dfrac{1}{2})^{99}$ $→B<1$ Bình luận
$2B=1+\dfrac{1}{2}+(\dfrac{1}{2})^2+…+(\dfrac{1}{2})^{98}$
$2B-B=[1+\dfrac{1}{2}+(\dfrac{1}{2})^2+…+(\dfrac{1}{2})^{98}]-[\dfrac{1}{2}+(\dfrac{1}{2})^2+…(\dfrac{1}{2})^{99}]$
$B=1-(\dfrac{1}{2})^{99}$
$→B<1$
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