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\(A=\frac{\left[\left(25-1\right):1+1\right]\left(25+1\right)}{2}=325.\)
\(B=\frac{\left[\left(51-3\right):2+1\right]\left(51+3\right)}{2}=675\)
\(C=\frac{\left[\left(81-1\right):4+1\right]\left(81+1\right)}{2}=861\)
1, Ta có :
\(x+\frac{3}{5}=\frac{4}{7}\div\frac{8}{21}\)
\(x+\frac{3}{5}=\frac{4}{7}\times\frac{21}{8}\)
\(x+\frac{3}{5}=\frac{3}{2}\)
\(x=\frac{3}{2}-\frac{3}{5}\)
\(x=\frac{15}{10}-\frac{6}{10}\)
\(x=\frac{9}{10}\)
Vậy x = \(\frac{9}{10}\)
2, Ta có :
\(\frac{2}{3}+\frac{3}{4}\div x=-\frac{1}{6}\)
\(\frac{3}{4}\div x=-\frac{1}{6}-\frac{2}{3}\)
\(\frac{3}{4}\div x=-\frac{1}{6}-\frac{4}{6}\)
\(\frac{3}{4}\div x=-\frac{5}{6}\)
\(x=\frac{3}{4}\div\left(-\frac{5}{6}\right)\)
\(x=\frac{3}{4}\times\left(-\frac{6}{5}\right)\)
\(x=-\frac{9}{10}\)
Vậy x = \(-\frac{9}{10}\)
1.
2|x-6|+7x-2=|x-6|+7x
2|x-6| - |x-6|=7x-(7x-2)
|x-6| = 2
=>x-6 = +2
*x-6=2 *x-6 = -2
x =2+6 x = (-2)+6
x =8 x = 4
2.
|x-5|-7(x+4)=5-7x
|x-5|-7x-28 =5-7x
|x-5|-28 =5-7x+7x
|x-5|-28 = 5
|x-5| = 5+28
|x-5| = 33
=>x-5 = +33
*x-5=33 *x-5=-33
x =38 x = -28
3.
3|x+4|-2(x-1)=7-2x
3|x+4|-2x+2 =7-2x
3|x+4|-2 =7-2x+2x
3|x+4|-2 =7
3|x+4| =7+2
3|x+4| = 9
|x+4| =9:3
|x+4| = 3
=>x+4 = +3
*x+4=3 *x+4=-3
x =-1 x = -7
a) \(\dfrac{3}{8}+\dfrac{15}{-25}+\dfrac{3}{5}\)
\(=\dfrac{-9}{40}+\dfrac{3}{5}\)
\(=\dfrac{3}{8}\)
b) \(\dfrac{-5}{18}+\dfrac{23}{45}-\dfrac{9}{10}\)
\(=\dfrac{7}{30}-\dfrac{9}{10}\)
\(=\dfrac{-2}{3}\)
c) \(\dfrac{-5}{12}+\dfrac{15}{18}-2,25\)
\(=\dfrac{5}{12}-2,25\)
\(=\dfrac{-11}{6}\)
d) \(\dfrac{5}{6}+\dfrac{2}{3}-0,5\)
\(=\dfrac{3}{2}-0,5\)
\(=1\)
ta có:
\(17.4+\frac{17}{34}.15\)
=\(68+7,5\)
=\(75,5\)
HOK TỐT