在一个半径为20米的圆形花坛周围栽树,每隔6.28米栽一棵树,一共可以栽多少棵树?
20×2×3.14÷6.28,
=20×6.28÷6.28,
=20(棵);
答:一共可以栽20棵树.
已知a>0,a2-2ab+c2=0,bc>a2.试比较a,b,c的大小.
Peter has _____ English friend.
He's _____ and helpful. [ ]
A. an, polite
B. an, politely
C. a, politely