b) 5( 2x + 3 )( x + 2 ) - 2( 5x - 4 )( x - 1 ) = 75
<=> 5( 2x2 + 7x + 6 ) - 2( 5x2 - 9x + 4 ) = 75
<=> 10x2 + 35x + 30 - 10x2 + 18x - 8 = 75
<=> 53x + 22 = 75
<=> 53x = 53
<=> x = 1
c) 2x2 + 3( x - 1 )( x + 1 ) = 5x( x + 1 )
<=> 2x2 + 3( x2 - 1 ) = 5x2 + 5x
<=> 2x2 + 3x2 - 3 - 5x2 - 5x = 0
<=> -3 - 5x = 0
<=> -5x = 3
<=> x = -3/5
b, \(5\left(2x+3\right)\left(x+2\right)-2\left(5x-4\right)\left(x-1\right)=75\)
\(\Leftrightarrow10x^2+20x+15x+30-10x^2+10x+8x-8=75\)
\(\Leftrightarrow53x+22=75\Leftrightarrow x=1\)
c, \(2x^2+3\left(x-1\right)\left(x+1\right)=5x\left(x+1\right)\)
\(\Leftrightarrow2x^2+3x^2+3x-3x-3=5x^2+5x\)
\(\Leftrightarrow5x^2-3=5x^2+5x\Leftrightarrow x=-\frac{3}{5}\)