F.2 Maths

radius = the base of an isosceles triangle, with two others side 6cm and angles 40, 70 70

so (radius / 2) / 6 = sin(40/2)
radis = 12*sin20 ~= 4.1042417199080247965291953761871cm

2007-05-16 15:10:11 補充：
請幻想一下一個兩邊一齊打開o左o既圓規佢會型成一個等邊三角形只要搵到呢個三角形o既底, 就搵到佢畫o既圓形o既半徑

the length of each arm of a pair of compasses is 6 cm.If the between the are is 40degree,find the radius of the circle drawn.

Let X be the radius of the circle drawn.
2X*π*40/360=6
X=6/2/π/40*360
X=8.594 (corr to 3d.p.)
∴the radius of the circle drawn is 8.594.

From the problem, we have a triangle with 2 sides of length 6cm and the 3rd side with an unknown length. Instead of considering this triangle as a whole, we can divide it into 2 triangles. So we have 2 right triangles with its hypotenuse of length 6cm, a 20-degree angle and a right angle. Then by the properties of the right triangle, we know that the oppsite side of the 20-degree angle will have length (6*sin(20 degrees))cm. Since this is only half the length (we divided the triangle into 2), the length of the unknown side of the entire triangle will be (2*(6*sin(20 degrees))) cm.

2*3.14*6*40/360
=4.19cm
I think it will you.

2007-05-12 12:51:13 補充：
呢個應該係答案，準確至三位有效數字我係中三仔阿(好似無關係)

I don't understand what is the question.
I think you have typed wrongly.
Please check it!!