test test: |S1Q|²=R²−x² |S2Q|²=r²−x² d1²=R²−x²+|QP|² d2²=r²−x²+|QP|² |AP|²=d1²−R² |BP|²=d2²−r² |AP|²=R²−x²+|QP|²−R² |AP|²=−x²+|QP|² |BP|²=r²−x²+|QP|²−r² |BP|²=−x²+|QP|² |AP|²=|BP|² |AP=|BP|