Using a Model

Part of the Graphs of Trig Functions section of Coddy's Trigonometry journey. Lesson 43 of 51.

In the harbour where d = 3cos(30°×t) + 7, the depth at 1 a.m. comes from t = 1:

d = 3cos(30°) + 7

cos(30°) = √(3)/2, so the depth is 7 + 3√3/2, about 9.598, which rounds to 9.60 m. Keep the exact value to the end and round once.

On the board the time arrives as its own line. Substitute it into the model, then round.

Challenge

On the coast with one tide a day from the last lesson, the depth is d = 2cos(15°×t) + 3 metres, t hours after high water. How deep is the water 5 hours after high water? Round to two decimal places. Press Check.

Try it yourself

d = 2cos(15°*t) + 3t = 5

Solve for d

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

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