Bài 2: Tìm x biết:

a, \(2^x+2^{x+1}+2^{x+2}+2^{x+3}=480\) \(\Rightarrow\) \(2^x.\left(1+2+2^2+2^3\right)=480\) \(\Rightarrow\) \(2^x.15=480\) \(\Rightarrow\) \(2^x=480:15\) \(\Rightarrow\) \(2^x=32\) \(\Rightarrow\) \(2^x=2^5\) \(\Rightarrow\) \(x=5\)

Bài 1: Tính hợp lý:

d. \(\dfrac{3}{2^2}.\dfrac{8}{3^2}.\dfrac{15}{4^2}...............\)\(\dfrac{899}{30^2}\) = \(\dfrac{1.3}{2.2}.\dfrac{2.4}{3.3}.\dfrac{3.5}{4.4}..............\dfrac{29.31}{30.30}\) = \(\dfrac{1.2.3.....29}{2.3.4.....30}.\dfrac{3.4.5.....31}{2.3.4.....30}\) = \(\dfrac{1}{30}.\dfrac{31}{2}\) = \(\dfrac{31}{60}\)

Ta có: \(x\div\frac{8}{3}=8\Rightarrow x=8.\frac{8}{3}\Rightarrow x=\frac{64}{3}\)

Bài 1: Tính hợp lý:

b. \(\dfrac{7}{12}+\dfrac{5}{6}+\dfrac{1}{4}-\dfrac{3}{7}-\dfrac{5}{12}\) = \(\left[\left(\dfrac{7}{12}-\dfrac{5}{12}\right)+\dfrac{5}{6}\right]+\dfrac{1}{4}-\dfrac{3}{7}\) = \(\left(\dfrac{1}{6}+\dfrac{5}{6}\right)+\dfrac{1}{4}-\dfrac{3}{7}\) = \(1+\dfrac{1}{4}-\dfrac{3}{7}\) = \(\dfrac{5}{4}-\dfrac{3}{7}\) = \(\dfrac{23}{28}\)

1.Tính hợp lý:

a. 1152 - (374 + 1152) + (374 - 65) = 1152 - 374 - 1152 + 374 - 65 = ( 1152 - 1152 ) + ( -65) + ( 374 - 374 ) = 0 + ( - 65) + 0 = -65

nhớ tick cho mk nha

Ta có: ab+ba=a.10+b+b.10+a=a.11+b.11=(a+b).11 chia hết cho 11

=>ab+ba chia hết cho 11

Nhớ tick cho mk nha

Question 1: Fill in the blank : a) PEACH b) BANANA

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