maths ]]]]

唔好意思.
唔太肯定你既y 係代表 angle ABD 定係 angle ABC

其實 如果係求 angle ABD 唔洗理其它角度係幾多
因為 ( angle in semi-circle ) 已經證明左 y 係90度

所以 angle CAD = 180度 - angle ABD - angle BAD - angle BDA
= 180 - 90 - 38 - 38
= 14 度 (angle sum of triangle)

所以 angle CBD 都係 14 度
by (Alt. Angle of Cyclic Quad.)
ie. angle ABC = 90+14 = 104度
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如果唔跟圖入面既角度 用你provide 既角度黎計
angle ADB = angle CDB = 25度
angle ABD = 90 度 ( 同上 )
甘......
angle CBD = 180 - angle ABD - angle ADB - angle CDB
= 180 - 90 - 25 - 25
= 40度 (Sum of Opposite Angles of a Cyclic Quad.)
而 angle ABC = angle ABD + angle CBD = 90 + 40 = 130 度