Pengaruh doping silver (Ag) terhadap sifat listrik dan efek magnetoresistansi material La0,8-xAgxCaO,2MnO3 (x = 0; 0,05; 0,1; 0,15) dengan metode sol-gel = The effect of silver ag doping on electrical property and magnetoresistance La0,8-xAgxCaO,2MnO3 (x = 0; 0,05; 0,1; 0,15) material by sol gel method