Toán Lớp 7: b,3×(-2)^(5x+13)+24=0 c,x+4/-12=-3/x+4

Question

Toán Lớp 7:  b,3×(-2)^(5x+13)+24=0 c,x+4/-12=-3/x+4

doanthulan · Answer

b)  3 xx ( -2 )^[ 5x + 13 ] + 24 = 0         3 xx ( -2 )^[ 5x + 13 ] = -24         ( -2 )^[ 5x + 13 ] = -24 : 3         ( -2 )^[ 5x + 13 ] = -8         ( -2 )^[ 5x + 13 ] = ( -2 )&sup3;         5x + 13 = 3         5x = 3 - 13         5x = -10         x = -2    ______________________________________   c)  [ x + 4 ] / [ -12 ] = [ -3 ] / [ x + 4 ]        ( x + 4 ) ( x + 4 ) = ( -3 ) . ( -12 )        x ( x + 4 ) + 4 ( x + 4 ) = 36        x&sup2; + 8x + 16 = 36        x&sup2; + 8x - 20 = 0        x&sup2; - 2x + 10x - 20 = 0        x ( x - 2 ) + 10 ( x - 2 ) = 0        ( x - 2 ) ( x + 10 ) = 0      $ left[ begin{matrix} x - 2 = 0    x + 10 = 0  end{matrix} right.$     $ left[ begin{matrix} x = 2    x = -10  end{matrix} right.$    Vậy  x = 2  hoặc  x = -10