x^-7x+12=a^-7a+12=>x^-7x=a^-7a=>x^-a^-7x-7a=0=>(x-a)(x+a)-7(x-a)=0=>(x-a)(x+a-7)=0=>x=a or x=7-aokmaybe i can not see this again,but i want to tell you .this very diffecult ,because i use my mobile fi...