题目

如图，E=6V，r=4Ω，R1=2Ω，R2的阻值变化范围是    0～10Ω．求：                            （1）电源的最大输出功率；                                                                                         （2）R1上消耗的最大功率；                                                                                        （3）R2上消耗的最大功率解方程组：3(x-1)=y+55(y-1)=3(x+5)．