用两面夹定理完全可证(sinx)/x=π/180(x趋向0,x为弧度)
用两面夹定理完全可证(sinx)/x=π/180(x趋向0,x为弧度).
证明:设圆的半径为r,x为弧度,圆心角为x*180/π,则(圆心角所对应的弦三角形面积)小于(圆心角所对应扇形面积)小于(圆心角所对应的外切三角形面积),即(1/2*r^2*sin(x*180/π))小于(πr^2*x*180/π/360)小于(1/2*r*2r*tg(x*180/π/2)),由此可得,(sin(x*180/π))/(x*180/π)小于或等于π/180(x趋向0),即(sinx)/x小于或等于π/180,(sin(x*180/π/2))/(x*180/π/2)大于或等于π/180(x趋向0),即(sinx)/x大于或等于π/180,由两面夹定理得:(sinx)/x=π/180(x趋向0,x为弧度)。
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