a: \(\Leftrightarrow\left(2x+5\right)-2\left(2x+5\right)\left(x-10\right)=0\)
=>(2x+5)(1-2x+20)=0
=>(2x+5)(21-2x)=0
=>x=-5/2 hoặc x=21/2
b: =>(x+5)(4x-1-x+5)=0
=>(x+5)(3x+4)=0
=>x=-5 hoặc x=-4/3
c: =>6x-18-(x-3)(x+2)=0
=>(x-3)(6-x-2)=0
=>(x-3)(4-x)=0
=>x=3 hoặc x=4

