如图,□ABCD中,AD︰AB=5︰4,过点A作AE⊥BC,AF⊥CD,垂足分别为E、F,AE=4cm,求AF的长.
(1)计算:(2)解方程:
计算:2sin60°+cos60°-3tan30°.
解方程:x2-6x-7=0.
计算:
计算:.