Homework Help: Math

Posted by Jon on Thursday, February 14, 2008 at 1:00pm.

There are no typos and no work b/c I don't know how to do them. Thanks.

1)Find cos theta if sin theta=3/5 and 90 degrees<theta<180 degrees.
A)4/5
B)-4/5
C)square root of 34/5
D)-square root of 34/5
I chose A

2)Simplify:1-csc^2theta/cot^2theta
A)-1
B)1
C)tan^2theta
D)1/sin^4theta
I chose C

3)Simplify:-5(cot^2theta-csc^2theta)
A)5
B)-5
C)-5csc^2 theta
D)5csc^2 theta
I chose B

4)Which expression is not equivalent to 1?
A)sin^2theta+cot^2thetasin^2theta
B)sin^2theta/1-costheta -1
C)sec^2theta+tan^2theta
D)cot^2thetasin^2theta/cos^2theta
I don't know C?

5)Which expression is equivalent to tan theta-sec theta/sin theta?
A)-cot theta
B)cot theta
C)tan theta-cot theta
D)tan theta-sec^2theta
I don't know

6)Find the exact value of cos375 degrees.
A)square root of 6 - square root of 2 over 4
B)square root of 6 + square root of 2 over 4
C)square root of 2 - square root of 6 over 4
D)- square root of 2 - square root of 6 over 4
I chose B

Math - drwls, Thursday, February 14, 2008 at 1:25pm
1) Wrong. Cosines are negative in the second quadrant.

2) Wrong. (1-csc^2x)/cot^2x
= [(sin^2x-1)/sin^2x]*sin^2x/cos^2x
= -cos^2/cos^2 x = -1

3) Wrong. -5(cot^2x - csc^2 x)
= -5(cos^2x -1)/sin^2x
= -5(-sin^2x/sin^2x)= +5

4) Correct. Sec^2 is always 1 or greater. Adding tan^2 makes it even larger.

Please show your work on the others, so we can see where you are making your other mistakes.
Math - Jon, Thursday, February 14, 2008 at 1:31pm
I dont know what im doing on these I don't even know where to begin. The whole thing is confusing
Math - Jon, Thursday, February 14, 2008 at 1:36pm
I have one:
1)Find cos theta if sin theta=3/5 and 90 degrees<theta<180 degrees.
A)4/5
B)-4/5
C)square root of 34/5
D)-square root of 34/5
I chose A

cos^2theta+sin^2theta=1
cos^2theta=1-sin^2theta
cos^2theta=1-(3/5)^2
cos^2theta=1-9/25
cos^2theta=16/25
=4/5

thats the only one that I can show work for.
Math - drwls, Thursday, February 14, 2008 at 5:19pm
I already answered #1 for you and explained why it is wrong. You cannot have a positive cosine for angles between 90 and 180 degrees.

You are not going to learn the subject if someone else does all the problems for you. Please post the problems one at a time and go through as many stps as you can. You need to review the subjects of trigonometric identities and the signs of trig functions in the various quadrants. Drawing a figure is a big help.
trignometry - b, Thursday, October 23, 2008 at 6:16pm
find the exact value of sec theta?
uhdayjsoz eoiutn - uhdayjsoz eoiutn, Sunday, February 1, 2009 at 9:24pm
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