24.4弧长和扇形面积(国外英语资料).docVIP

24.4弧长和扇形面积(国外英语资料) Arc length and fan area Guidance of learning Thinking integration Analytic emphasis 1. arc length formula and its application N represents the multiples of the center angle of 1 degrees. It is without units. At the same time, third quantities can be found for any two quantities in the formula L, N, and R [1] (1) if the radius is 6cm, then the 240 degree angle of the arc length is __. (2) if an arc arc length is 2 pi cm, the center of the arc angle is 72 degrees, so that the arc radius is __. Coaching equation is an important tool to deal with many computational geometry, geometric formula and theorem provides a stage for the application of the equation. In L, N, R three in the amount of the thought and method of equations, the two known amount for third. 2. fan area formula and its application Not only can grasp and application, but also to understand the derivation formula of the area of the sector. It should also master the calculation method of some combination of graphics area, namely by the conversion method, the combination of graphics will be divided into a plurality of rules and graphics or difference. This problem combines the area of regular polygon, arc length, fan area and composite figure. It should learn to decompose the graph properly so that the problem can be further simplified I calculate the perimeter and area in the combination of graphics processing, should circle center and radius, clarify each arc angle, do not blindly to calculate. [cases] 4 figure 24 - 4 - 3, the O string AC = 2cm / ABC = 45 DEG, graph in the shaded area. Connect OA, CO. Dreams / ABC = 45 DEG L / AOC = 90 degrees. In Rt AOC, AO = CO, AC = 2, I find the shaded area can be flexibly cut up into regular graphics graphics area at the same time, should pay attention to the application of circular angle theorem. Side area and full area of 3. cone The side of the cone is a curved surface, and the expansion is a sector with a radius of the bus, [case 5] make a co