trig questions

1. the expression tan (180 degrees +x) is equivalent to

( i don't know how to read and solve this expression since i dont know about what is x)

a. tan x
b. cot x
c. -tan x
d. -cot x
x is a variable and tan(180+x)=tan x
The answer is a

2. express sin (360 degrees - x) as a function of positive actue angle
sin(360-x)=-sin x

3.the expression cos (pie - X) is equivalent to

a. cos x
b. -sinx
c. -cos x
d. sin x
cos(pie-x)=-cos x .
The answer is C

4. if Θ is an obtuse angle and sin Θ= b, then it can be concluded that

a) cos 2 Θ > b
b) cos Θ> b
c) sin2Θ<b
d) tan Θ>b
Θ is an obtuse angle and sin Θ= b
So b>0
Now 90<Θ<180
180<Θ<360
So
cos 2 Θ > b may not be true
cos Θ> b should be wrong
sin2Θ<b should be true
tan Θ>b should be wrong



2008-11-25 02:54:08 補充：
4 ANSWER C

無計架。你自己看本數學書死記公式啦

Q4.
If sin x = b and x is an obtuse angle. b must be a positive number because sine in 2nd quadrant is always positive.
(b) and (d) are certainly wrong because cos x and tan x in the 2nd quadrant are always negative.
(c) is certainly correct because sin 2x is either in the 3rd or 4th quadrant. sine in these 2 quadrants are always negative, so must be less than b.
(a) could be correct or wrong depending on x, if x < 150, it is wrong, if x > 150 it is correct.