Trigonometric Functions Help!!

[Taihenkoichi]

---

Members don't see this ad.

Any one have any good online resources for practicing trigonometric functions? I really don't understand how the functions are related. Is there an easy rule to memorize that will help me with all functions. Obviously I know SOHCAHTOA, but that doesn't help me answer a question like 'Which of the following is true for all values of x such that 0<x<pi/2 ?
a. sin x = cos^2 +1
b. tan x = (sin x)(cos x)
c. tan x = cos x/ sinx
d. sin^2 x = 1 - cos^2 x
e. sin x = 1/ cos x

 

[Blarelli]

http://www.sosmath.com/trig/Trig5/trig5/trig5.html

As far as I know, D is the only one of those listed that is an actual pathagorean identity. That link shows a bunch of different identities.

 

[Streetwolf]

Any one have any good online resources for practicing trigonometric functions? I really don't understand how the functions are related. Is there an easy rule to memorize that will help me with all functions. Obviously I know SOHCAHTOA, but that doesn't help me answer a question like 'Which of the following is true for all values of x such that 0<x<pi/2 ?
a. sin x = cos^2 +1
b. tan x = (sin x)(cos x)
c. tan x = cos x/ sinx
d. sin^2 x = 1 - cos^2 x
e. sin x = 1/ cos x

A: sin(x) - cos^2(x) = 1 *makes no sense*
B: tan(x) = sin(x)cos(x) *it is tan = sin/cos so this is wrong*
C: tan(x) = cos(x) / sin(x) *see above... this is cotangent here*
D: sin^2(x) + cos^2(x) = 1 *classic identity, this is correct*
E: sin(x) = 1/cos(x) *this is the definition of secant, not sine*

So if choice D doesn't jump out at you, you need to eliminate others. You can EASILY eliminate B, C, and E because these are definitions gone wrong. For example in B they use the wrong symbol (multiply instead of divide) and in C they use the wrong trig function (tan instead of cot).

So you can narrow it down to A and D and from there you could try plugging in some values until one of them works in D and not in A.

 

[Taihenkoichi]

any websites with practice problems??

 

[keliao]

D .is correct