[tatari/nightmare]

15.Let ABC be an acute triangle.The bisecter of angle ACB intersects AB at point L.The feet of the perpendicular from L
to AC and BC are denoted by M and N respectively.Let P be the intersecting point of AN and BM.Prove that CP is perpendicular to AB
16.In $\bigtriangleup$ABC ,$\angle ABC=60^{\circ}$ and $\angle ACB=70^{\circ}$.Point D is on the line segment BC such that $\angle BAD=20^{\circ}$.Prove that $AB+BD=AD+DC$
หมายเหตุ:ข้อ 16 กรุณาคิดวิธีที่ไม่ใช้ Trigo ด้วย