又問數 [復制鏈接]

In the figure, AB isd a diameter. CD is a chord parallel to AB. If arcAC = 1/2arcCD

a) express Y in terms of X
b) find X and Y

(a) since arcAC = 1/2arcCD
    so 2y=x(arc proportional to < at 圓周....)

(b)add a line BC
  <ACB=90'(< in semi. circle)
 
  <DAB=x(corr. <s,CD//AB)
  <ABC=x(<s in the same segment)
   
    so, <ACB+<DAB+<ABC+y=180'(< sum of triangle)
          90'+   x   +   x   +2x=180'
          x=22.5'
          y=2x=45'

又thz