what happened here (black marker)?why wasnt 2h eliminated, and where did 2, 1 and -3 go?

Example: Find the slope of the tangent line at point (1,3) on the curve f (x) = 2x + x2 m = lim f(1+h)-f(1) h-0 h m = lim 12(1+h)+(1+h)=]-[3] h-0 h m = lim 2+2h+1+2h+h2-3 h-0 h m = limb+4h h-0 h lim ( h + 4 ) h-0 m = 4 The slope of the tangent line at point (1,3) on the curve f (x) = 2x + x2 is 4. Notice that we found the slope of this same curve using the secant method in a previous example. The results are exactly the same. However, the First Principles Method is definitely more efficient