Tìm số tự nhiên x, biết:
a) 123 – 5(x+4) = 38 b) \((3{\rm{x}} - {2^4}){.7^3} = {2.7^4}\)
a) 123 – 5(x+4) = 38 \( \Leftrightarrow \) 5(x+4) = 123 – 38
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\( \Leftrightarrow \) 5(x+4) = 85 \( \Leftrightarrow \) x + 4 = 85 : 5 \( \Leftrightarrow \) x + 4 = 17
\( \Leftrightarrow \) x = 17 – 4 \( \Leftrightarrow \) x = 13
b)
\(\eqalign{
& (3{\rm{x}} - {2^4}){.7^3} = {2.7^4} \Leftrightarrow 3{\rm{x}} - {2^4} = {2.7^4}:{7^3} \cr
& \Leftrightarrow 3{\rm{x}} - 16 = 2.7 \Leftrightarrow 3{\rm{x}} - 16 = 14 \Leftrightarrow 3{\rm{x}} = 14 + 16 \cr
& \Leftrightarrow 3{\rm{x}} = 30 \Leftrightarrow x = 30:3 \Leftrightarrow x = 10 \cr} \)