Tangent Lines to Exponential and Logarithmic Functions through the Origin
For each exponential function , draw the tangent line through the origin. The points of tangency lie on the horizontal line Likewise, for the logarithmic functions , the points of tangency lie on the vertical line .
Reference: H. Skala, "A discover-e," The College Mathematics Journal, 28(2), 1997 pp. 128–129.