已知圆的周长为90厘米，求直径可以给出计算过程么 已知周长，求直径怎么算？
\u5df2\u77e5\u5706\u7684\u5468\u957f\u4e3a90\u5398\u7c73,\u6c42\u76f4\u5f84\u5468\u957f\u7b49\u4e8e\u03c0\u4e58\u4ee5\u76f4\u5f84\uff0c90=3.14*D\uff0cD\u7ea6\u7b49\u4e8e28.7
\u7531\u4e8e\u5df2\u77e5\u5468\u957fC\uff0c\u4e14\u5706\u7684\u5468\u957f\u516c\u5f0f\u4e3aC=2\u03c0r\u6216\u8005C=\u03c0d\uff0c\u7531C=\u03c0d\u5f97\u5230\u5706\u7684\u76f4\u5f84\u4e3ad=C/\u03c0\u3002
\u6269\u5c55\u8d44\u6599\u5706\u7684\u5468\u957f=\u5706\u5468\u7387\u00d7\u76f4\u5f84\u2192C=\u03c0d
\u5706\u7684\u5468\u957f=\u5706\u5468\u7387\u00d72\u00d7\u534a\u5f84\u2192C=2\u03c0r
\u5706\u7684\u9762\u79ef=\u5706\u5468\u7387\u00d7\u534a\u5f84\u7684\u5e73\u65b9\u2192S=\u03c0r^2
\u534a\u5706\u7684\u9762\u79ef:S\u534a\u5706=(\u03c0r^2)/2
\u534a\u5706\u7684\u5468\u957f:d+(\u03c0d)/2\u6216\u8005d+\u03c0r
\u73af\u9762\u79ef: S\u5927\u5706-S\u5c0f\u5706=\u03c0(R^2-r^2)(R\u4e3a\u5927\u5706\u534a\u5f84\uff0cr\u4e3a\u5c0f\u5706\u534a\u5f84)
\u6ce8:S:\u9762\u79ef\u3001 C:\u5468\u957f\u3001 d=\u76f4\u5f84\u3001 r=\u534a\u5f84\u3001d=2r\u3002\u5706\u5468\u7387:\u03c0(\u6570\u503c\u4e3a3.1415926\u81f33.1415927\u4e4b\u95f4\u2026\u2026\u65e0\u9650\u4e0d\u5faa\u73af\u5c0f\u6570)\uff0c\u901a\u5e38\u91c7\u75283.14\u4f5c\u4e3a\u03c0\u7684\u6570\u503c
所以 直径=圆的周长除以派
=90/π
=-28.66厘米（π取3.14，精确到百分位）。
πd=c，d=90/π
绛旓細鍛ㄩ暱绛変簬蟺涔樹互鐩村緞锛90=3.14*D锛孌绾︾瓑浜28.7
绛旓細鎵浠 鐩村緞=鍦嗙殑鍛ㄩ暱闄や互娲 =90/蟺 =-28.66鍘樼背锛埾鍙3.14锛岀簿纭埌鐧惧垎浣嶏級銆
绛旓細28.66鍘樼背銆傚懆闀90鍘樼背鐩村緞绾︿负28.66鍘樼背銆傚渾鐨勫懆闀垮叕寮忎负C绛変簬2蟺r锛屾墍浠绛変簬C/2蟺锛屾墍浠ョ洿寰刣绛変簬r+r绛変簬r+C/2蟺绛変簬C/蟺+C/2蟺绛変簬C/蟺涔1+C/2蟺涔1/蟺绛変簬C/蟺涔橈紙1+1/蟺锛夌瓑浜90/3.14涔橈紙1+1/蟺锛夆増90/3.14鈮28.66锛堝帢绫筹級銆
绛旓細鏍规嵁鍛ㄩ暱鍏紡銆傚懆闀跨瓑浜庣洿寰勪箻浠ュ渾鍛ㄧ巼锛屾墍浠ャ鍛ㄩ暱涓90鍘樼背锛岀洿寰绛変簬90梅3.14鈮28.67鍘樼背銆
绛旓細28.7鍘樼背銆傛牴鎹暟瀛﹁绠楁樉绀猴紝鍦嗙殑鍛ㄩ暱C绛変簬90鍘樼背锛屽渾鐨勫崐寰勪负R鍘樼背锛岀洿寰勬槸D绛変簬2R鍘樼背锛岄氳繃璁＄畻锛氬渾鐨勫懆闀跨瓑浜2涔樹互鍦嗗懆鐜囦箻浠ュ崐寰凴绛変簬2涔樹互鍦嗗懆鐜囦箻浠ュ崐寰凴绛変簬鐩村緞D涔樹互鍦嗗懆鐜囷紝鍒欑洿寰凞绛変簬鍗婂緞C闄や互鍦嗗懆鐜囩瓑浜90鍘樼背闄や互3.14绛変簬28.7鍘樼背銆
绛旓細3.14脳90=282.6鍘樼背 鐩村緞鎵鍦ㄧ殑鐩寸嚎鏄渾鐨瀵圭О杞淬傜洿寰勭殑涓や釜绔偣鍦ㄥ渾涓婏紝鍦嗗績鏄洿寰鐨勪腑鐐广傜洿寰勫皢鍦嗗垎涓洪潰绉浉绛夌殑涓ら儴鍒,涓棿鐨勭嚎娈靛氨鍙洿寰勶紙姣忎竴涓儴鍒嗘垚涓轰竴涓崐鍦嗭級銆
绛旓細90cm鐨勫渾鐩村緞鏄90/3.14=28.66鍘樼背銆備笌鍦嗙浉鍏崇殑鍏紡锛1銆佸渾闈㈢Н锛歋=蟺r²锛孲=蟺(d/2)²銆傦紙d涓虹洿寰勶紝r涓哄崐寰勶級銆2銆佸崐鍦嗙殑闈㈢Н锛歋鍗婂渾=(蟺r^2)/2銆傦紙r涓哄崐寰勶級銆3銆佸渾鐜潰绉細S澶у渾-S灏忓渾=蟺(R^2-r^2)(R涓哄ぇ鍦嗗崐寰勶紝r涓哄皬鍦嗗崐寰)銆4銆佸渾鐨勫懆闀匡細C=2蟺r鎴朿=蟺d...
绛旓細鍦嗙殑鍛ㄩ暱L鍏紡鏄疞 = 2蟺r 鎴栬 L =蟺l,鍏朵腑蟺涓哄渾鍛ㄧ巼,鏄竴涓父鏁, 绾︿负3.141592654, r涓哄渾鐨勫崐寰, l涓哄渾鐨鐩村緞銆1銆佸埌瀹氱偣鐨勮窛绂荤瓑浜庡畾闀跨殑鐐圭殑闆嗗悎鍙綔鍦嗐傝繖涓畾鐐瑰彨浣滃渾鐨勫渾蹇冿紝閫氬父鐢ㄥ瓧姣嶁渙鈥濊〃绀恒2銆佽繛鎺ュ渾蹇冨拰鍦嗗懆涓婁换鎰忎竴鐐逛箣闂寸殑杩炵嚎鍙綔鍗婂緞锛岄氬父鐢ㄥ瓧姣嶁渞鈥濊〃绀恒3銆侀氳繃...
绛旓細鏍戝共涓鍛ㄧ殑闀垮害鏄90鍘樼背锛岄偅涔堣鏄庢爲骞茬殑鍛ㄩ暱鏄90鍘樼背锛屾垜浠妸瀹冪湅鎴愭槸涓涓渾杩戜技鐨勫渾锛岄偅涔堟牴鎹懆闀跨瓑浜幭涔樹互鐩村緞锛岄偅涔堢洿寰勫氨搴旇鏄90梅3.14=28.66锛鎵浠ュ畠鐨勭洿寰勫ぇ绾︽槸28.66鍘樼背銆
绛旓細鏍规嵁鍦嗗懆闀鐨勮绠楀叕寮忥細C=pai *d锛涙墍浠鐩村緞鐨=鍛ㄩ暱C/鍦嗗懆鐜囷紱鍗筹細鐩村緞涓猴細60cm/3.14=19.1cm銆
