Math Destroyer Test 9, help!

[Bigbirdo]

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1. For question 28 in test 9, why doesn’t the formula P(A or B) = P(A) + P (B) – P(A and B) work? If I do that, I got 100%, which is obviously wrong.

2. For question 37 in test 9, how do you turn [sin(x)-cos(x)]/cos(x)] to Tan (x) – 1? Is this a formula? Are there similar formulas like this?

3. For question 39 in test 9, is the answer C or D? From the explanation, it seems to be D, but then answer is C?

 

[Bigbirdo]

Anybody?

 

[Illfavor]

For 28, you're massively overthinking it. 17% of them are both, so 83% are either/or, but not both.

For 37, you need to learn the pythagorean trigonometric functions in general, but for here you just have to know that sec(x) = 1/cos and sin/cos = tan

39 is D, one of many misprints I believe.

 

[shulace]

For question 37, it's easier to solve if you split the fraction: [sin(x)-cos(x)]/cos(x)] into [sin(x)/cos(x)-(cos(x)/cos(x))]. Can you see how it becomes tan(x)-1 now?

 

[KyoPhan]

I also got D for 39.