​a2​+a6​=225​a3​×a5​=25=a2​×a6​=a42​a42​=25⇒a4​=5a2​&a6​ are roots of x2−225​x+25=0x=25​,10a2​=25​,a6​=10a4​=5a4​=a2​r2⇒5=25​r2⇒r2=2a8​=a6​r2=10×2=20a4​+a6​+a8​=5+10+20=35​