亚洲激情+欧美激情,无码任你躁久久久久久,我的极品美女老婆,性欧美牲交在线视频,亚洲av高清在线一区二区三区

電子課本網(wǎng) › 第63頁

第63頁

信息發(fā)布者：
解：?$(1)\ \mathrm {a}(a-2b)+2b(a-2b)=(a+2b)(a-2b) $?
?$a^2-4b^2=(a+2b)(a-2b)$?
?$(2)$?當?$a=63.5m，$??$b=18.25m$?時，
?$(a+2b)(a-2b)=(63.5+2×18.25)(63.5-2×18.25)$?
?$ =(63.5+36.5)(63.5-36.5)$?
?$ =2700(\mathrm {m^2})$?
?${\frac {1} {4}}\pi ab$?
C
解：?$(1)S_1={\frac {1} {2}}\pi r^2-2×{\frac {1} {2}}\pi {({\frac {1} {2}}r)}^2={\frac {1} {2}}\pi r^2-{\frac {1} {4}}\pi r^2={\frac {1} {4}}\pi r^2$?
?$(4)\ \mathrm S_2={\frac {1} {2}}\pi r^2-{\frac {1} {2}}\pi {({\frac {r+c} {2}})}^2-{\frac {1} {2}}\pi {({\frac {r-c} {2}})}^2$?
?$ ={\frac {1} {2}}\pi r^2-{\frac {1} {8}}\pi (r^2+2rc+c^2)-{\frac {1} {8}}\pi (r^2-2rc+c^2) $?
?$ ={\frac {1} {4}}\pi r^2-{\frac {1} {4}}\pi c^2$?
∵?$c>0$?
∴?$ S_1>S_2$?
上一頁 下一頁