(1)
x^2/a^2+y^2/b^2=1
b^2x^2+a^2y^2=a^2b^2
x+y-1=0
y=-x+1
将y=-x+1,代入b^2x^2+a^2y^2=a^2b^2,
b^2x^2+a^2(-x+1)^2=a^2b^2,
即(b^2+a^2)x^2-2a^2x+a^2-a^2b^2=0,
x1+x2=2a^2/(b^2+a^2),
x1*x2=(a^2-a^2b^2)/(b^2+a^2),
∵OP⊥OQ,
∴x1*x2+y1*y2=0,
即x1*x2+(x1-1)*(x2-1)=0
∴2x1*x2-(x1+x2)+1=0,
∴2a^2-2a^2b^2-2a^2+b^2+a^2=0,
得,
b^2+a^2=2a^2b^2,
即1/a^2+1/b^2=2,
(2)
e^2=1-a^2/b^2=1+1/(1-2a^2),
∵1/2≤e^2≤3/4,
∴3≤2a^2≤5,
∴长轴范围是√6≤2a ≤√10