3*16^x+2*81^x=5*36^x3*4^2x+2*9^2x=5*(4^x)(9^x) 等式两边同除以4^2x ,化简得2(9/4)^2x-5(9/4)^x+3=0[2(9/4)^x+1][(9/4)^X-3]=0, 而2(9/4)^x+1≠0∴(9/4)^X-3=0∴(9/4)^X=3x=log(9/4)(3)
