例1(1)(2016·高考全国卷乙) Delta ABC 的内角A,B,C的对-|||-边分别为a,b,c.已知 =sqrt (5) =2, cos A=dfrac (2)(3), 则 b= ()-|||-A. sqrt (2) B. sqrt (3) C.2 D.3-|||-(2)(2016·高考全国卷丙)在 Delta ABC 中, =dfrac (pi )(4), BC边上的-|||-高等于 dfrac (1)(3)BC, 则 sin A= ()-|||-A. dfrac (3)(10) B. dfrac (sqrt {10)}(10) C. dfrac (sqrt {5)}(5) D. dfrac (3sqrt {10)}(10)-|||-(3)(2016·高考全国卷甲) Delta ABC 的内角A,B,C的对边分-|||-别为a,b,c,若 cos A=dfrac (4)(5) cos C=dfrac (5)(13) ,=1, 则 b=