Use the method of Example 1 to calculate the slope of the line tangent to the curve of each of the given functions. Let Q1
have the indicated x-values. Sketch the curve and tangent lines.
![](https://test.transtutors.com/qimg/c381f7ae-21b9-4d1d-b93b-b8add47b0f0c.png)
EXAMPLE 1 Limit of slopes of secant lines
Find the slope of a line tangent to the curve y = x2 + 3x at the point P (2,10) by finding the limit of the slopes of the secant lines PQ as Q approaches P. Let point Q have the x-values of 3.0, 2.5, 2.1, 2.01, and 2.001. Then, using a calculator, we tabulate the necessary values. Because P is the point (2,10) x1 = 2 and y1 = 10. Thus, using the values of x2we tabulate the values of
and thereby the values of the slope m:
![](https://test.transtutors.com/qimg/b5d0aa4f-42d0-4894-ae67-12d7aa4ee074.png)
We see that the slope of PQ approaches the value of 7 as Q approaches P. Therefore, the slope of the tangent line at (2, 10) is 7. See Fig. 23.15.
![](https://test.transtutors.com/qimg/781cfbaa-3800-4a0c-96bb-d07c063cd719.png)