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Câu 14:
a. \(\text{3 + x = - 8}.\) \(\Leftrightarrow x=-8-3=-11.\)
b. \(\text{(35 + x) - 12 = 27}.\)
\(\Leftrightarrow35+x=27+12.\)
\(\Leftrightarrow35+x=39.\Leftrightarrow x=39-35=14.\)
c. \(2^x+15=31.\)
\(\Leftrightarrow2^x=16.\)
\(\Leftrightarrow2^x=2^4.\)
\(\Leftrightarrow x=4.\)
a, (-20) + 16 + (-34) + 20 = [(-20) + 20] + [16 + (-34)] = 0 + (-18) = (-18) b, 12 + 3.[39 - (5 - 2)2] = 12 + 3.[39 - 32] = 12 + 3.[39 - 9] = 12 + 3.30 = 12 + 90 = 102
a: Số số hạng là:
(40-2):2+1=20(số)
Tổng là:
42x10=420
Gọi C=\(\frac{\frac{2}{39}-\frac{1}{15}-\frac{2}{153}}{\frac{1}{34}+\frac{3}{20}-\frac{3}{26}}:\frac{1+\frac{2}{71}-\frac{5}{121}}{\frac{65}{121}-\frac{26}{71}-13}\)
=\(\frac{\frac{-4}{9}\cdot\left(\frac{1}{34}+\frac{3}{20}-\frac{3}{26}\right)}{-\left(\frac{1}{34}-\frac{3}{20}-\frac{3}{26}\right)}:\frac{1+\frac{2}{71}-\frac{5}{121}}{-13\cdot\left(\frac{2}{71}-\frac{5}{121}+1\right)}\)
=\(-\frac{4}{9}:-\frac{1}{13}=-\frac{4}{9}\cdot\left(-13\right)=\frac{\left(-4\right)\cdot\left(-13\right)}{9}=\frac{52}{9}\)
a) \(...=-\dfrac{12}{46}-\dfrac{15}{21}+\dfrac{3}{7}-\dfrac{7}{23}\)
\(=-\dfrac{12}{46}-\dfrac{7}{23}-\dfrac{15}{21}+\dfrac{3}{7}\)
\(=-\dfrac{6}{23}-\dfrac{7}{23}-\dfrac{5}{7}+\dfrac{3}{7}\)
\(=-\dfrac{13}{23}-\dfrac{2}{7}\)
\(=-\dfrac{13.7}{23.7}-\dfrac{2.23}{23.7}\)
\(=-\dfrac{91}{161}-\dfrac{46}{161}=-\dfrac{137}{161}\)
b) \(...=-21+\dfrac{7}{9}-\dfrac{3}{17}+\dfrac{25}{9}\)
\(=-21-\dfrac{3}{17}+\dfrac{7}{9}+\dfrac{25}{9}\)
\(=-21-\dfrac{3}{17}+\dfrac{32}{9}\)
\(=-\dfrac{3213}{153}-\dfrac{27}{153}+\dfrac{544}{153}=-\dfrac{2696}{153}\)
\(b,\left(-26\right)+16+\left(-34\right)+26=\left(-10\right)+\left(-8\right)=-18\\ c,12+3.\left[39-\left(5-2\right)^2\right]\\ =12+3.\left[39-3^2\right]\\ =12+3.\left[39-9\right]\\ =12+3.30\\ =12+90=102\)
b) (-26)+16+(-34)+26
=16-34
=-18
c)12+3[39-(5-2)2]
=12+3[39-(25-20+4)]
=12+3[39-9]
=12+3.30
=12+90
=102