maths

MC answer(D)
一個簡單的方法：劃一個△XYZ，x、y、和z分別系三隻對應角啦
sin x=YZ/XY
cos x=XZ/XY
sin y=XZ/XY=cos x
cos y=YZ/XY=sin x
tanx=YZ/XZ
tany=XZ/YZ
∵x y z are the angles of a triangle and x+y=90
∴z=180-(x+y)=90
∴sinz=sin90=1 cosz=cos90=0
A.
LHS
=tanxtany
=1
=sin90
=sinz
=RHS
B.
LHS
=cosy+cosz
=cosy+0
=sinx
=RHS
C.
LHS
=sin^2x+sin^2y
=sin^2+cos^2x
=1
=sin^2z
=RHS

1.
the volume of hemisphere
=(1/2)(4∏r^3/3)
=2∏r^3/3
the volume of cylinder
=∏r^2h
so
2∏r^3/3=∏r^2h
r:h=3:2