f(x)=√2*(2x-π/4)/sin(x+π/2)
∵cosa=3/5
∴a=arccos3/5
f(a)
=√2*(2a-π/4)/sin(a+π/2)
=√2*(2arccos3/5-π/4)/cosx
=√2*(2arccos3/5-π/4)*5/3
f(x)=√2*(2x-π/4)/sin(x+π/2)
∵cosa=3/5
∴a=arccos3/5
f(a)
=√2*(2a-π/4)/sin(a+π/2)
=√2*(2arccos3/5-π/4)/cosx
=√2*(2arccos3/5-π/4)*5/3