Toán Lớp 6: a, (321)+135-(51+135-321)
b,18.(-21)+21.(-128)+(-21).(-146)
c,321-[123-(72-6.9) mũ 2+(-56)]
bài 2:tìm x
a,2x+(-132)=27-(-143)
b,372-x=-2.31
c,|2x+13|=(-3).(-15)
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Toán Lớp 6: a, (321)+135-(51+135-321)
b,18.(-21)+21.(-128)+(-21).(-146)
c,321-[123-(72-6.9) mũ 2+(-56)]
bài 2:tìm x
a,2x+(-132)=27-(-143)
b,372-x=-2.31
c,|2x+13|=(-3).(-15)
Comments ( 2 )
$a) (-321)+135-(51+135-321)$
$=-321+135-51-135+321$
$=(-321+321)+(135-135)-51$
$=0+0-51$
$=-51$
$b) 18.(-21)+21.(-128)+(-21).(-146)$
$=(-18).21+21.(-128)+21.146$
$=21.(-18-128+146)$
$=21.0$
$=0$
$c,321-[123-(72-6.9)^{2}+(-56)]$
$=321-[123-18^{2}+(-56)]$
$=321-[123-324-56]$
$=321-(-257)$
$=321+257$
$=578$
$\text{Bài 2: Tìm x}$
$a)2x+(-132)=27-(-143)$
$⇒2x-132=27+143$
$⇒2x-132=170$
$⇒2x=170+132$
$⇒2x=302$
$⇒x=302:2$
$⇒x=151$
$\text{Vậy $x$ = 151}$
$b,372-x=-2.31$
$⇒372-x=-62$
$⇒x=372+62$
$⇒x=434$
$\text{Vậy $x$ = 434}$
$c,|2x+13|=(-3).(-15)$
$⇒|2x+13|=3.15$
$⇒|2x+13|=45$
$⇒$\(\left[ \begin{array}{l}2x+13=45\\2x+13=-45\end{array} \right.\)
$⇒$\(\left[ \begin{array}{l}2x=45-13\\2x=-45-13\end{array} \right.\)
$⇒$\(\left[ \begin{array}{l}2x=32\\2x=-58\end{array} \right.\)
$⇒$\(\left[ \begin{array}{l}x=32:2\\x=-58:2\end{array} \right.\)
$⇒$\(\left[ \begin{array}{l}x=16\\x=-29\end{array} \right.\)
$\text{Vậy }$ $x∈$ {$16; -29$}
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