Question

Tìm x, biết :

a) 71 + ( 26 - 3x ) : 5 = 75

b) 20 - [ 7 ( x - 3 ) + 4 ] = 2

c) 3^x . 2 + 15 = 33

d) 720 : 14  [ 41 - ( 2x - 5 ) ] = 2³ . 5

Answer 1

\(71+\left(26-3x\right)\div5=75\)

\(\left(26-3x\right)\div5=4\)

\(26-3x=20\)

\(3x=6\Leftrightarrow x=2\)

Answer 2

\(20-\left[7\left(x-3\right)+4\right]=2\)

\(7x-21+4=18\)

\(7x-17=18\)

\(7x=25\Leftrightarrow x=\frac{25}{7}\)

Answer 3

\(3^x.2+15=33\)

\(3^x.2=18\)

\(3^x=9\Leftrightarrow x=2\)

Answer 4

\(720\div14\left[41-\left(2x-5\right)\right]=2^3.5\)

\(720\div14\left[41-2x+5\right]=40\)

\(14\left(46-2x\right)=18\)

\(46-2x=\frac{9}{7}\)

\(2x=\frac{313}{7}\Leftrightarrow x=\frac{313}{14}\)