已知非零有理数x、y满足
,则
=__________.
如图,已知∠DCE=∠A=90°,BE⊥AC于B,且DC=EC,BE=8cm,则AD+AB=_____ .

计算:
__________.
把实数0.0000907用科学记数法表示为_______________.
如图,在五边形ABCDE中,AB=AC=AD=AE,且AB∥ED,∠EAB=120°,则∠DCB=( )

A.150° B.160° C.130° D.60°
若a+b=3,ab=2,则a-b的值为( )
A. 1 B. ±1 C. -1 D. ![]()
