定义域就是
2sinx != 0=> sinx != 0 -> x != k*pi
pi是圆周率
cosa = 3/5
立即要盯困想到直角三角形三边是3,4,5
于是又sina = 4/5
sin 2a = 2sina*cosa = 2 * 3/5 *4/5 = 24/25
cos 2a = (cosa)^2 - (sina)^2 = 9/25 - 16/25 = - 7/25
所野察以f(a) = (24/25 - (-7/25)) / 2 * 4/颂则茄5 = 31/40
(1)2sinx不等伏橘于0
即x不等兄厅羡于k派
(2)依题意,sina=4/5
即sin2x=24/25
cos2x=-7/25
故羡拍f(a)=31/40
1,定义域:x不等于π/2+2kπ
2,31/40