Phần típ theo nè!
Câu 5: Tìm \(x\):
Đề bài : \(xxx\) - \(x
\) x 105 = 30
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Câu 6: Tìm \(x \):
a) \(x \) x 7 + \(x\) = 384.
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b) \( x\)\(x
\) - \(x\) x 2 = 378.
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Câu 7: Tìm số tự nhiên ab biết ab x 9 = 2ab :
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Câu 8: Viết biểu thức sau thành tích 2 thừa số:
Đề bài: ab + ab x 2 + ab x 4 + ab =
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-------- Còn nữa -------
(x + 1) + (x + 4) + (x + 7) + (x + 10) + .... + (x + 28) = 155 (có 10 số hạng ở vế trái)
=> x + 1 + x + 4 + x + 7 + x + 10 + .... + x + 28 = 155
=> (x + x + x + ... + x) + (1 + 4 + 7 + 10 + ... + 28) = 155
10 hạng tử 10 hạng tử
=> \(10\times x+10\times\left(28+1\right):2=155\)
=> \(10\times x+145=155\)
=> \(10\times x=10\)
=> x = 1
(x+1)+(x+4)+.......+(x+28)=155
=> x+x+.....+x+1+4+......28=155
=>10x+(28+1):2*10=155
=> 10x+145=155
=>10x=10
=>x=1
vậy x=1