中4maths 7B 1(c),2(c),6,7,8

1c)TA=TB (tangent property) a=4

AB=TB(given) TA=TB=AB
so angle ABT=60度 eq. triangle (唔記得長寫..都唔記得reason..你搵下你本書有冇laa..冇記錯如果呢本冇果個reason ge..本5C係有gaa..)
angle OBT=90度 (tangent property)
b=90-60=30度

2008-01-10 05:08:11 補充：
2c)angle OAC=angle OCA=b (base angle, isos triangle)...OA=OC=radiusangle OAT=90度 (tangent property)angle ATO=angle BTO=52/2=26度 (tangent property)angle ATO angle OAT angle OAC angle OCA=180度 (angle sum of triangle)26 90 b b=180b=32度

2008-01-10 05:08:56 補充：
6)我見到你都寫左BR=RC=PC=AP=5cm我唸你應該都識搵哂佢地出黎..d reasons都係(tangent property) la..then..angle PAC=angle PCA (base angle, isos triangle)2angle PAC+60=180 (angle sum of triangle)angle PAC=angle PCA =60度因為3個角都60度..所以係eq. triangle.因為係eq. triangle..所以AC=AP=CP=5cm

2008-01-10 05:09:31 補充：
7a)ZB=BX(tangent property)用(base angle, isos triangle)同 (angle sum of triangle)..你就會搵到angle ZXB=64度angleYXC=180-64-44=72度 (adj.angles in str. line)angleYXC=angleXYC=72度(tangent property)angleYCX=36度 (angle sum of triangle)7b)angle ZYX=angleZXB=64度 (冇記錯ge話個reason好似係..angle in alt. angle)

2008-01-10 05:09:55 補充：
8a)因為arc ratio=angle in center ge ratio..(reason自己搵書)所以angle AOB=360/3=120度8b)angle AOC=angle COB (tangent property)so angle AOC=120/2=60度8c)angle CDB=angle COB/2 (angle at center twice at circumference)angle CDB=60/2=30度