At 90 degrees, the drawn figure is a straight triangle with three centers connected, ab=6, ac=8, bc= 10, so the angle a=90. The common tangents of AB and AC are perpendicular to AB and AC respectively, so a square will be formed, so x=90. I put the picture in Baidu space. It's a little small. You can have a look at/674323010/album/item/b289b54b319ebc45f3a2b8226cffc1716b3.html.