抛物線x^2 = 8(y-b)在點(4,b+2)處切線斜率怎麼求 RT

抛物線x^2 = 8(y-b)在點(4,b+2)處切線斜率怎麼求 RT

x^2 = 8(y-b)
y=x^2/8+b
求導:y'=2x/8=x/4
x=4時,斜率k=y'=4/4=1