Help with this question please.

[nickglyn]

Hey, so I'm 100% confused as how to do part part ii and iii. What the hell do they mean by low tide?

Much appreciated!

[jakesilove]

Hey, so I'm 100% confused as how to do part part ii and iii. What the hell do they mean by low tide?

Much appreciated!

Hey! Low tide is going to be the minimum height of the water. We know that the minimum value of sin(anything) is -1, therefore the minimum height will be 1+0.7(-1)=0.3m

For the second part, you just need to solve when the height is 1.35. You'll get two values for the time, and the solution will be between those two times! Draw yourself a graph, and put a dotted line at 1.35m. You'll see the intercepts clearly; you're looking for the portion of the graph above that line.

Let me know if you want a proper worked solution, or if this is enough info!

[nickglyn]

I tried doing it your way but I wasn't sure how to get the intercepts :/ I had a look at the sample answers and I don't get what they really mean, can you help explain how you did it your way and how they did it?

[jamonwindeyer]

I tried doing it your way but I wasn't sure how to get the intercepts :/ I had a look at the sample answers and I don't get what they really mean, can you help explain how you did it your way and how they did it?

I'll let Jake explain his way, but what they've set up in your image is a simple inequality. The LHS is the height, and the RHS is the requirement of 1.35 metres. They are solving for values of t which gives a value of height that is enough for the condition to be satisfied! Notice how from second to third line, they give the angle range that puts the sine ratio to a value of one half or greater

[jakesilove]

I tried doing it your way but I wasn't sure how to get the intercepts :/ I had a look at the sample answers and I don't get what they really mean, can you help explain how you did it your way and how they did it?

My way is exactly the same as theirs, except instead of an inequality, I would just set h=1.35. Then I would solve for values of t, and decide whether the answer was WITHIN the two values for t, or OUTSIDE of the two values for t (by testing a point between, and a point outside). They are literally the same methods Just set up the equation, set h=1.35m, and solve for t

[nickglyn]

Okay I'm understanding it a lot more now, thank you both for your help. But quick question, how did you guys know in this question to draw the sine graph to get the answer? I understand why you did it, but I worry that if I'm under exam conditions I won't think ways to get the answer like that.

[RuiAce]

Okay I'm understanding it a lot more now, thank you both for your help. But quick question, how did you guys know in this question to draw the sine graph to get the answer? I understand why you did it, but I worry that if I'm under exam conditions I won't think ways to get the answer like that.

Because solving a trigonometric inequality is ridiculous using algebraic approaches. The rule of ASTC becomes much harder when you have inequalities as opposed to an equation.

You can do it algebraically, but it is extremely hard and unlikely that a 2U student would be expected to do it so easily. The geometric (sine graph) approach is a visual aid for you here.

Fact: When the algebraic approach gets too hard, attempt a geometric approach.

[nickglyn]

Alrighty cheers to all of you for the help!