if cos+cos2? =1 then prove that sin12?+3sin10?+3sin8?+sin6?+ 2sin4?+2sin2?-2=1 2. sec?=x+{1/4x}prove that sec?+tan?=2x or(1/2x) 3. cosec?-sin?=L and sec?-cos? =m,then prove that L2m2(L2+m2+3)=1 4. prove that the external bisector of an angle of a triangle divides the opposite side externally in the ratio of the sides containing the angle. 5. o is ay point inside a triangle ABC.The bisector OD,OE and OF of angle AOB,BOC,COA meets the sides AB,BC and CA in the point D,E,F respectively.Show that AD*BE*CF=DB*EC*FA. please give the answers as soon as possible as the day after tomorrow is my maths exam and there is no mistake in a quetions