Given: circle o with diameter ln and inscribed angle lmn prove: is a right angle. what is the missing reason in step 5? statements reasons 1. circle o has diameter ln and inscribed angle lmn 1. given 2. is a semicircle 2. diameter divides into 2 semicircles 3. circle o measures 360o 3. measure of a circle is 360o 4. m = 180o 4. definition of semicircle 5. m∠lmn = 90o 5. ? 6. ∠lmn is a right angle 6. definition of right angle hl theorem inscribed angle theorem diagonals of a rhombus are perpendicular. formed by a tangent and a chord is half the measure of the intercepted arc.