# Trig Identities

posted by .

Please help...I'm not understanding trig identities and how to manipulate and express these two problems in their associated functions.

Thanks

a)Express as a function of cos (theta)

2 sin^2(theta) - 1

b)Express as a function of sin (theta) or cos (theta)

tan^2(theta) - 2 sec(theta)sin(theta)

• Trig Identities -

I will use x instead of theta for easier typing

2 sin^2 x - 1 = cos 2x
do you have to prove this?
if so, then

RS = -cos(2x)
= -cos(x+x)
= -cosxcosx + sinxsinx
= -cos^x + sin^x
= -(1-sin^x_ + sin^x
= 2sin^x - 1
= LS

• Trig Identities -

for the second

tan^x - 2secxsinx
= sin^2 x/cos^2 x - 2sinx/cosx
= sin^2 x/cos^2 x 2 sinxcosx/cos^2 x
= (sin^2 x - sin 2x)/(1 - sin^2 x)

this is in terms of sinx

## Similar Questions

1. ### trig

express 20sin theta + 4 cos theta as R sin(theta + alpha) R sin(theta + alpha) = R cos(alpha)sin(theta) + R sin(alpha)cos(theta) ----> Rcos(alpha) = 20 Rsin(alpha) = 4 The x-y coordinates of a point on a circle of radius R that …
2. ### trig

Work out the following identities a) sin theta/cos theta b) tan theta cos theta
3. ### Trig Identities

a)Express as a function of cos (theta) 2 sin^2(theta) - 1 b)Express as a function of sin (theta) or cos (theta) tan^2(theta) - 2 sec(theta)sin(theta)
4. ### Trigonometry

I don't understand how I'm supposed set the problem up or what theta is... Use the given function value(s), and trigonometric identities (including the cofunction identities), to find the indicated trigonometric functions. sec theta …
5. ### trigonomtry

can you correct the rest for me please? Express each as a function of theta: a. sin (270deg + theta)= cos theta b. cos (pi + theta)= -cos theta c. tan (810 + theta)= ?
6. ### trigonometry

can you correct the rest for me please? Express each as a function of theta: a. sin (270deg + theta)= cos theta b. cos (pi + theta)= -cos theta c. tan (810 + theta)= ?
7. ### trigonometry

can you correct the rest for me please? Express each as a function of theta: a. sin (270deg + theta)= cos theta b. cos (pi + theta)= -cos theta c. tan (810 + theta)= ?
8. ### trig

in proving trigonometric identities if cot theta sin theta = cos theta. what is the correct answer?
9. ### trig

in proving trigonometric identities if sec theta - tan theta sin theta is equal to cos theta. what is the correct answer?
10. ### Trig

Simplify each expression using fundamental identities. 1. Sin theta cot theta 2. 1-sin^2 theta / cos theta

More Similar Questions