Thực hiện phép tính sau đây:
A.( 30 ×5)+56
B. (60.30):(3×3)
C(.76+5.×4) -39
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a) - 2 3 .125.32. ( − 76 ) > 0 12.74 . - 3 4 . ( − 395 ) < 0 ⇒ ( − 2 ) 3 .125.32. ( − 76 ) > 12.74. ( − 3 ) 4 . ( − 395 )
b) ( − 1 ) . ( − 2 ) . ( − 3 ) ... ( − 20 ) > 0 ( − 3 ) . ( − 4 ) . ( − 5 ) ... ( − 23 ) < 0 ⇒ ( − 1 ) . ( − 2 ) . ( − 3 ) ... ( − 20 ) > ( − 3 ) . ( − 4 ) . ( − 5 ) ... ( − 23 )
A= -1 + -1 + -1 +....+ -1
so chu so -1 la { (76-1):1+1}:2=38
A=-38
a, A = ( 1/3 + 12/67 + 13/41 ) - ( 79/67 - 28/41 )
A = (\(\frac13\) + \(\frac{12}{67}\) + \(\frac{13}{41}\)) - (\(\frac{79}{67}\) - \(\frac{28}{41}\))
A = \(\frac13\) + \(\frac{12}{67}\) + \(\frac{13}{41}\) - \(\frac{79}{67}\) + \(\frac{28}{41}\)
A = - (\(\frac{79}{67}-\frac{12}{67}\)) + (\(\frac{13}{41}\) + \(\frac{28}{41}\))
A = - 1 + 1 + \(\frac13\)
A = 0 + \(\frac13\)
A = \(\frac13\)
b, B = 3/4×7 + 3/7×10 + 3/10×13 + ......+ 3/73×76
B = \(\frac{3}{4\times7}\) + \(\frac{3}{7\times10}\) + \(\frac{3}{10\times13}\) + ... + \(\frac{3}{73\times76}\)
B = \(\frac14-\frac17\) + \(\frac17-\frac{1}{10}\) + ... + \(\frac{1}{73}-\frac{1}{76}\)
B = \(\frac14\) - \(\frac{1}{76}\)
B = \(\frac{19}{76}-\) \(\frac{1}{76}\)
B = \(\frac{18}{76}\)
B = \(\frac{9}{38}\)
5^2.53-50.17+25.3^4
=25.53-25.2.17+25.81
=25(53+81-34)
=25(134-34)
=25.100=2500
A=(30x5)+56=150+56=206
B=(60x30):(3x3)=1800:9=200
C=(76+5x4)-39=(76+20)-39=86-39=47