Can someone help me and verify if the answer I picked is correct?

Question

1. Which function does not have a maximum value?

a) x^2 + 9
b) g(x) = 9 - x - x^2
c) h(x) = -(x+1)^2
d) k(x) = -4 + x - x^2

The answer is A because letter b,c,d opens the parabola downwards?

Myra is riding a Ferris Wheel. Her height h(t), in metres above the ground at time t seconds, can be modeled by
h(t) = 10sin(6(t - 20°)) + 10. At what time will Myra's car be at its greatest height?

a) t=20 s
b) t=35 s
c) t=40 s
d) t=55 s

Is it C?

3. At which point on the graph of f(x)= -x^2 - 2x +15 is the slope of the tangent 0?

a) (-2, 15)
b) (-1,16)
c) (0,15)
d) (3,0)

Help~

Answer 1

1 and 3 are correct

2. First of all do not put a ° symbol behind the 20, that makes no sense,
10 sin(6(t-20)) + 10 has a maximimum value of 20 when sin(6(t-20)) is 1
we know sinπ/2 = 1, so 6(t-20) = π/2
t-20 = π/12
t = 20 + π/12 = 20.26

Whoever made up this equation does not seem to understand that if t is defined in seconds, then you cannot use degrees in the equation, yet if t=35
then we get 10sin(6(35-20)+10 = 10(sin 90) + 10 = 20
But the 90 would have to be degrees and the 35 was in seconds. What a mess-up!

The equation is bogus, and makes no sense.

Answer 2

Thanks~ I understand #2 now.

If I have more questions, do I post them here or post a new question?