對于拋物線y^2=4x上任意一點Q，點P（a，0）滿足絕對值PQ大于等于絕對值a，則a的取值范圍
熱心網友
點Q在拋物線y^2=4x上，設其坐標為：Q(y^2/4,y)|PQ| = |a| === |PQ|^2 = a^2 == (y^2/4 - a)^2 + (0 - y)^2 = a^2== (y^2)*(y^2 -8ay +16) = 0== y^2 -8ay +16 = 0若y取任意值，上式都成立，則：判別式 -1 < a < 1
對于拋物線y^2=4x上任意一點Q，點P（a，0）滿足絕對值PQ大于等于絕對值a，則a的取值范圍
點Q在拋物線y^2=4x上，設其坐標為：Q(y^2/4,y)|PQ| = |a| === |PQ|^2 = a^2 == (y^2/4 - a)^2 + (0 - y)^2 = a^2== (y^2)*(y^2 -8ay +16) = 0== y^2 -8ay +16 = 0若y取任意值，上式都成立，則：判別式 -1 < a < 1