(x-3)2-x(x-8),
=x2-6x+9-x2+8x,
=2x+9.
当x=2-4时,原式=2(2-4)+9=22+1.
He_____ articles for our wall-newspaper these years, and he____ about thirty articles.
A.has written; wrote
B.has been writing; wrote
C.is writing; has been writing
D.has been writing; has written
用于判定高压灭菌效果,包裹中心可放置()
A.明矾
B.硫磺
C.高锰酸钾
D.氢氧化钾
E.碳酸氢钠