about a ninth-grade geometry problem
My brother asked me this problem, and he is studying ninth-grade. I can't solve it using primitive tools of pure geometry. Hope someone can give me a hint to solve it. Thanks.
Given a circle $(O, R)$ and $A$ is outside $(O)$ such that $OA > 2R$. Draw two tangents AB, AC of $(O)$. Let $I$ is midpoint of AB. Segment OI intersects with (O) at M. AM intersects with (O) at N, $N \neq M$. NI intersects with BC at Q. Prove that MQ perpendicular with OB
Here is the picture
This is NOT a solution. I just want to share some of my findings.
Construction: 1) Extend BO to cut the red circle at D; 2) DA cut the red circle at E and BM extended at F; 3) OE is joined.
By midpoint theorem, we have 1) OMI // DEFA; 2) BJ = JE; BM = MF.
All angles marked with the same color are equal.
OJMI is the line of centers of the 4 circles and BJHE is the common chord (excluding the green).
H is the orthocenter of the isosceles triangle DBF.
B, G, H, and M lie on the green circle.
One way to get the Job done is by showing that MQ is parallel to either BI or GH.