A:have prepared
B:had prepared
C:have been preparing
D:was preparing
要使多项式x2- 12mxy-x+7y2+xy-x+1不含xy的项,那么m的值为( )
—What does she like doing?—She doesn't like playing the trumpet __________ the piano.
化简与求值:
(1)化简:1+tan15°1-tan15°;
(2)已知α,β都是锐角,cosα=17,cos(α+β)=﹣1114,求cosβ的值.
南京梅花山是全国著名的赏梅胜地之一,近年来,梅花山的植梅规模不断扩大,新的品种不断出现,如今的梅花山的梅树约15000株,这个数可用科学记数法表示为( )