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số sh cua tong A bang so hang cua day so cach deu 1 don vi tu 1 den 60
so sh cua tong A la:(60-1):1+1=60 (sh)
Cu 3 sh lien tiep cua tong A nhom thanh 1 nhom thi ta duoc so nhom la : 60: 3=20(nhom)
khi do : A = (2+2^2+2^3)+(2^4+2^5+2^6)+(2^7+2^8+2^9)+....+(2^58+2^59+2^60)
A=(2+2.2+2.2^2)+(2^4+2^4.2+2^4.2^2)+(2^7+2^7.2+2^7.2^2)+.....+(2^58
2^58.2+2^58.2^2)
A=2(1+2+2^2)+2^4(1+2+2^2)+2^7(1+2+2^2)+...+2^58(1+2+2^2)
A=2.7+2^4.7+2^7.7+...+2^58.7
A=7(2+2^4+2^7+...+2^58)
Vi 7 chia het cho 7
2+2^4+2^7+...+2^58 thuoc N
Suy ra 7(2+2^4+2^7+...+2^58) chia het cho 7
hay A chia het cho 7
Vay A chia het cho 7
Câu 1:
abc >/ 100 ; bca >/ 100 ; cab>/100
< = > abc + bca + cab >/300
< = > abc + bca + cab >/ 111
a) (-5) + (-10) + 20
= 20 - 5 - 10
= 5
b) 29 + (-40) + (-12)
= 29 - 40 - 12
= -23
c) 58 + (-14) + (-73)
= 58 - 14 - 73
= -29
\(a\text{)}\left(-5\right)+\left(-10\right)+20\)
\(=\left(-15\right)+20\)
\(=5\)
\(b\text{)}29+\left(-40\right)+\left(-12\right)\)
\(=\left(-11\right)+\left(-12\right)\)
\(=-23\)
\(c\text{)}58+\left(-14\right)+\left(-73\right)\)
\(=44+\left(-73\right)\)
\(=-29\)
\(\text{Hok tốt!}\)
\(\text{@Kaito Kid}\)
a) 53.(-15)+(-15).47
=53.[(-15)+(-15)].47
=53.(-30).47
=-1590.47
=-74730
a) \(\left(19x+2\cdot5^2\right):14=\left(13-8\right)^2-4^2\)
\(\Leftrightarrow\left(19x+2\cdot25\right):14=5^2-4^2\)
\(\Leftrightarrow19x+50=\left(25-16\right)\cdot14\)
\(\Leftrightarrow19x+50=9\cdot14\)
\(\Leftrightarrow19x+50=126-50\)
\(\Leftrightarrow19x=76\)
\(\Leftrightarrow x=76:19\)
\(\Leftrightarrow x=4\)
b) \(x+\left(x+1\right)+\left(x+2\right)+...+\left(x+30\right)=1240\)
\(\Leftrightarrow\left(x+x+x+x...+x\right)+\left(1+2+3+...+30\right)=1240\)
\(\Leftrightarrow31x+\frac{\left[\left(30-1\right):1+1\right]\cdot\left(30+1\right)}{2}=1240\)
\(\Leftrightarrow31x+465=1240\)
\(\Leftrightarrow31x=775\)
\(\Leftrightarrow x=25\)
c)\(11-\left(-53+x\right)=97\)
\(\Leftrightarrow-53+x=-86\)
\(\Leftrightarrow x=-33\)
d) \(-\left(x+84\right)+213=-16\)
\(\Leftrightarrow-\left(x+84\right)=-229\)
\(\Leftrightarrow x+84=229\)
\(\Leftrightarrow x=145\)
a.
\(180-\left(150.2+180.3-175.4\right)=180-\left(300+540-700\right)\)
\(=180-140=40\)
b. \(200:\left\{2.\left[32-\left(35-2^3\right)\right]+30\right\}=200:\left\{2.\left[32-\left(35-8\right)\right]+30\right\}\)
\(=200:\left\{2.5+30\right\}=200:40=5\)
1/ Bg
\(\frac{21^4}{27.\left(-343\right)}\)= \(\frac{\left(3.7\right)^4}{3^3.\left(-7\right)^3}\)
= \(\frac{3^4.7^4}{3^3.\left(-7\right)^3}\)
= \(\frac{3.\left(-7\right)}{1.1}\)
= 3.(-7)
= -21
2/ Bg
Ta có: \(\frac{a}{4}=\frac{b}{5}=\frac{c}{2}\)và a + b - c = 21 (a, b, c thuộc Z)
Áp dụng tính chất dãy tỉ số bằng nhau, ta có:
\(\frac{a}{4}=\frac{b}{5}=\frac{c}{2}=\frac{a+b-c}{4+5-2}=\frac{21}{7}\)= 3
=> a = 3.4 = 12
=> b = 3.5 = 15
=> c = 3.2 = 6
Vậy a = 12, b = 15 và c = 6
Đáp án: A
97 . 36 + 97 . 64 = 97.(36+64) = 97.100=9700