step1 draw a circle of radius 4.2 cm with center as O.                                        step 2 take  a point A on the circle and join OA . Draw a perpendicular to OA at point A.
step3 DRAW a radius OB making an angle of 90 degree with OA. 
step4 draw a perpendicular to OB at point B. let both the perpendicular  intersect at point P.PA and PB are required tangents at an angle at 45 degree.