17.已知tanα=3,计算:
(1)(4sinα-2cosα)/(5cosα+3sinα);
(2)sinα⋅cosα.
18.计算:(1)lg5+ln√("e" )+2^(-1+log_23 )+(lg2)^2+lg5⋅lg2.
(2)若2^a=5^b=10,求1/a+1/b的值.
19.已知α是第三象限角,f(α)=(sin(π-α)cos(2π-α)tan(-α-π))/(tan(-α)sin(-π-α)).
(1)化简f(α);
(2)若cos(α-3/2 π)=1/5,求f(α)的值;
20.已知函数f(x)=√2 cos(2x+π/4)+1
(1)求f(x)最小正周期;单调增区间
(2)求f(x)在区间[0,π/2]上的最大值和最小值.
21.已知f(x)=2^x+a(1/2)^x是偶函数.
(1)求a的值;
(2)判断当x>0时,函数的单调性(不用证明);
(3)解关于t不等式f(2t)≥f(t+1)