it is shown in calculus slope of line tangent to y=x^3 at point (a,a^3) has slope3a^2
find equation of line tangent to y=x^3 at (2,8) and (a, a^3)
At , the slope of the tangent line is . Now use your point-slope form, to form the equation of the tangent line. The second part can be done the same way.