I 31 - 17 I - I 13 - 57 I
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đáp án
𝑖31−𝑖13−69𝑖
@Xoài :) nhớ tuôi bên học 24 hong chắc hong nhớ :))))
Bài 1:
a: \(\Leftrightarrow\dfrac{2}{3}\cdot\dfrac{6+9-4}{12}< =\dfrac{x}{18}< =\dfrac{7}{13}\cdot\dfrac{3-1}{6}\)
\(\Leftrightarrow\dfrac{22}{36}< =\dfrac{x}{18}< =\dfrac{14}{78}=\dfrac{7}{39}\)
\(\Leftrightarrow\dfrac{11}{9}< =\dfrac{x}{9}< =\dfrac{7}{13}\)
=>143<=x<=63
hay \(x\in\varnothing\)
b: \(\Leftrightarrow\dfrac{31\cdot9-26\cdot4}{180}\cdot\dfrac{-36}{35}< x< \dfrac{153+64+56}{168}\cdot\dfrac{8}{13}\)
\(\Leftrightarrow-1< x< 1\)
=>x=0
a) \(30+\left(-30\right)+7\)
\(=30-30+7\)
\(=0+7\)
\(=7\)
b) \(12+\left(-31\right)\)
\(=12-31\)
\(=-31+12\)
\(=-\left(31-12\right)\)
\(=-19\)
c) \(\left(-40\right)+\left(-20\right)+\left(-40\right)\)
\(=-40-20-40\)
\(=-\left(40+20\right)-40\)
\(=-60-40\)
\(=-\left(60+40\right)\)
\(=-100\)
d) \(13+\left|-13\right|\)
\(=13+13\)
\(=26\)
e) \(\left|-13\right|+\left|-12\right|+\left|-17\right|\)
\(=13+12+17\)
\(=25+17\)
\(=42\)
f) \(-17+\left|-17\right|+12\)
\(=-17+17+12\)
\(=-\left(17-17\right)+12\)
\(=-0+12\)
\(=-\left(0-12\right)\)
\(=-\left(-12\right)\)
\(=12\)
31. a) \(\left(a+b\right)^3-3ab\left(a+b\right)\)
\(=a^3+3a^2b+3ab^2+b^3-3a^2b+3ab^2\)
\(=a^3+b^3\)
b) \(\left(a-b\right)^3+3ab\left(a-b\right)\)
\(=a^3-3a^2b+3ab^2-b^3+3a^2b-3ab^2\)
\(=a^3-b^3\)
Áp dụng: \(a^3+b^3\)
\(=\left(a+b\right)^3-3ab\left(a+b\right)\)
\(=-125+90\)
\(=-35\)
35. a) \(34^2+66^2+68.66\)
\(=34^2+2.34.66+66^2\)
\(=\left(34+66\right)^2=100^2=10000\)
b) \(74^2+24^2-48.74\)
\(=74^2-2.74.24+24^2\)
\(=\left(74-24\right)^2=50^2=2500\)
Nhớ tick
\(\left|31-17\right|-\left|13-57\right|=\left|14\right|-\left|-44\right|=14-44=-30\)
-44 oqr đâu đấy ạ