y=2^x-2^-x
=e^(xln2)-1/e^(xln2)
y'=ln2e^(xln2)+1/[e^(xln2)]^2*ln2e^(xln2)
=ln2*2^x+ln2*2^x/[2^x]^2
=ln2*2^x+ln2/2^x
【公式更快
y=a^x
y'=a^xlna