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692 + 152 - 92
= (692 - 92) + 152
= 600 + 152
752
Tính nhanh 692+152−92
692+152−92=(692−92)+152=600+152=752 ( Đúng )
\(692+152-92=692-92-152=600-152=752\)( Sai )
\(C=\frac{1}{2}+\frac{1}{14}+\frac{1}{35}+\frac{1}{65}+\frac{1}{104}+\frac{1}{152}\)
\(C=\frac{2}{4}+\frac{2}{28}+\frac{2}{70}+\frac{2}{130}+\frac{2}{208}+\frac{2}{304}\)
\(C=\frac{2}{1.4}+\frac{2}{4.7}+\frac{2}{7.10}+\frac{2}{10.13}+\frac{2}{13.16}+\frac{2}{16.19}\)
\(C=\frac{2}{3}.\left(\frac{3}{1.4}+\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+\frac{3}{13.16}+\frac{3}{16.19}\right)\)
\(C=\frac{2}{3}.\left(3-\frac{3}{4}+\frac{3}{4}-\frac{3}{7}+\frac{3}{7}-\frac{3}{10}+\frac{3}{10}-\frac{3}{13}+\frac{3}{13}-\frac{3}{16}+\frac{3}{16}-\frac{3}{19}\right)\)
\(C=\frac{2}{3}.\left(3-\frac{3}{19}\right)\)
\(C=\frac{2}{3}.\frac{54}{19}\)
\(C=\frac{36}{19}\)
mk sai bước cuối
\(C=\frac{2}{3}.\left(1-\frac{1}{4}+\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+\frac{1}{10}-\frac{1}{13}+\frac{1}{13}-\frac{1}{16}+\frac{1}{16}-\frac{1}{19}\right)\)
\(C=\frac{2}{3}.\left(1-\frac{1}{19}\right)\)
\(C=\frac{2}{3}.\frac{18}{19}\)
\(C=\frac{12}{19}\)
\(\dfrac{1}{2}+\dfrac{1}{14}+\dfrac{1}{35}+\dfrac{1}{65}+\dfrac{1}{104}+\dfrac{1}{152}\\ =\dfrac{2}{4}+\dfrac{2}{28}+\dfrac{2}{70}+\dfrac{2}{130}+\dfrac{2}{208}+\dfrac{2}{304}\\ =\dfrac{2}{3}\cdot\left(\dfrac{3}{4}+\dfrac{3}{28}+\dfrac{3}{70}+\dfrac{3}{130}+\dfrac{3}{208}+\dfrac{3}{304}\right)\\ =\dfrac{2}{3}\cdot\left(\dfrac{3}{1\cdot4}+\dfrac{3}{4\cdot7}+\dfrac{3}{7\cdot10}+\dfrac{3}{10\cdot13}+\dfrac{3}{13\cdot16}+\dfrac{3}{16\cdot19}\right)\\ =\dfrac{2}{3}\cdot\left(\dfrac{1}{1}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{13}+\dfrac{1}{13}-\dfrac{1}{16}+\dfrac{1}{16}-\dfrac{1}{19}\right)\\ =\dfrac{2}{3}\cdot\left(1-\dfrac{1}{19}\right)\\ =\dfrac{2}{3}\cdot\dfrac{18}{19}\\ =\dfrac{12}{19}\)
Bổ sung đề : Tính
\(\left(-152\right)-108.\left(-152\right)+7.\left(-152\right)\)
\(=\left(-152\right).\left(1-108+7\right)\)
\(=\left(-152\right).\left(-100\right)=15200\)
(-152) - 108. (-152) + 7. (-152)
= (-152) . (1 - 108 + 7)
= (-152) . (-100)
= 15200.
Chúc bạn học tốt !!!
\(C=\frac{1}{2}+\frac{1}{4}+\frac{1}{35}+\frac{1}{65}+\frac{1}{104}+\frac{1}{152}=\frac{431}{532}\)
Mình nghĩ là bằng 309
152 . 75 + ( 152 + 4 ) .25 = ( 152 . 3 ) . 25 + ( 152 + 4 ) .25
= 456 . 25 + 156 . 25
= 25 . ( 456 + 156 )
= 25 . 612
= 15300