By using the formula cos (A+B) = cos A cos B - sin A sin B , prove that cos A - cos 3A = 4 sin^2 A cos A

1 answer

well, how far did you get?

cos3A = cos(2A+A) = cos2A cosA - sin2A sinA
= (1-2Sin^2A)(cosA) - (2SinAcosA)(sinA)
try and finish it up from here

Similar Questions

expres the following as sums and differences of sines or cosinescos8t * sin2t sin(a+b) = sin(a)cos(b) + cos(a)sin(b) replacing

Top answer: Trigonometry was not discovered by a single person. Its development spans thousands of years and Read more.
Reduce the following to the sine or cosine of one angle:(i) sin145*cos75 - cos145*sin75 (ii) cos35*cos15 - sin35*sin15 Use the

Top answer: To reduce the given expressions to the sine or cosine of one angle, we can use the trigonometric Read more.
Given:cos u = 3/5; 0 < u < pi/2 cos v = 5/13; 3pi/2 < v < 2pi Find: sin (v + u) cos (v - u) tan (v + u) First compute or list

Top answer: if cos u=3/5 cos v=5/13 then sin u=4/5 and sin v=12/13 then sin(v+u)=sinv cos u+cos v sin u Read more.
Show that sin(x+pi)=-sinx.So far, I used the sum formula for sin which is sin(a+b)=sin a cos b+cos a sin b. sin(x+pi)=sin x cos

Top answer: in(x+pi)=sin x cos pi+cos x sin pi but cosPI=-1, sin PI=0 sin(x+PI)= -sinx Read more.
it says to verify the following identity, working only on one side:cotx+tanx=cscx*secx Work the left side. cot x + tan x = cos

Top answer: Great job figuring it out! It looks like you made a minor mistake in your simplification. Let me Read more.
Question: Trying to find cos π/12, if cos π/6 = square root 3 over 2, how to find cos π/12 using DOUBLE angle formula?This is

Top answer: you got it backwards π/12 = (1/2) of π/6 using cos 2A = cos^2 A - sin^2 A = 2cos^2 A - 1 so cos Read more.
I do not understand how to do this problem((sin^3 A + cos^3 A)/(sin A + cos A) ) = 1 - sin A cos A note that all the trig terms

Top answer: use graphic techiques in radians I found that it is roughly equal to -.5 sin [ 20.42036^-1(x + Read more.
Simplify the given expression........?(2sin2x)(cos6x) sin 2x and cos 6x can be expressed as a series of terms that involve sin x

Top answer: To simplify the expression (2sin2x)(cos6x), we can use the identity sin2x = 2sinxcosx. We start by Read more.
Determine the measure of side a ( to the nearest degree and minute).sin a = sin A cos B sin A = cos a cos B cos a = cos B/ sin A

Top answer: As \(\cos A = \frac{\cos a}{\sin B}\), \(\cos a = \cos A \cdot \frac{\sin B}{\cos B}\). Since Read more.
Which of the following equations is used to solve for side a?Determine the measure of side a ( to the nearest degree and

Top answer: The equation that is used to solve for side a is: cos a = cos A/ sin B Read more.