Ok, I've found the answer to these questions, but I did so in more of a trial and error way. The question is:(adsbygoogle = window.adsbygoogle || []).push({});

f(x) = 2x^2 + x

Find the two tangent lines to the curve, which both pass through the point (2,-3).

So, I tried using y=mx+b = 2x^2 + x, where m = f'(x) = 2x + 1, thus:

(2x+1)x + b = 2x^2 + x. I worked this out to find an extraneous answer, and one correct tangent of y = -x - 1. I know the other answer has a slope of 11, through trial and error, but there's got to be an easier way.

Any thoughts on how to do this algebraically?

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Pesky Tangents

**Physics Forums | Science Articles, Homework Help, Discussion**