Find the equation of the tangent to y = 2x^2 + 7 at x = 3.

The first step here is to identify what to do. Differentiating the equation y = 2x^2 + 7 will result in dy/dx = 4x. Given that you know that x = 3, you can substitute x = 3 into 4x which gives you 4(3) = 12. Thus, you now know that the gradient is equal to 12 at the point x = 3. However, you are trying to find the equation of the tangent and so you use the equation y = mx + c to calculate the equation. You know that the values are m = 12, x = 3 but y and c are currently unknown. To find the value of y, you substitute x = 3 into the original equation of y = 2x^2 + 7 which gives you y = 25. Plug in the values into y = mx + c to find c and rearrange to find c. c = 25 - 36 = -11. Finally, putting all of these values together results in y = 12x - 11.

Answered by Danielle C. Maths tutor

2932 Views

See similar Maths GCSE tutors

Related Maths GCSE answers

All answers ▸

Solve the equation 5(2c - 3) = 19


A farmer has 30 boxes of eggs. There are 6 eggs in each box. Write, as a ratio, the number of eggs in two boxes to the total number of eggs. Give your answer in its simplest form.


If f(x) = x^2, draw the graph of y = f(x) + 3


Frank buys a car at the start of 2015, for £12,000. Each year the value fo the car depreciates by 9%. What was the value of the car at the end of 2019?


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo
Cookie Preferences