SOLUTION: If cos54 = t, determine cos144 in terms of t

Question 1057159: If cos54 = t, determine cos144 in terms of t
Answer by ikleyn(52864) (Show Source): You can put this solution on YOUR website!
.
If cos(54�) = t, determine cos(144�) in terms of t
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Notice that  144� = 90� + 54�.


Based on it, I will find cos(144�) in one steps.


cos(144�) = cos(90�+54�) =  ( apply the formula cos(a+b) = cos(a)*cos(b) - sin(a)*sin(b) ) = 

            cos(90�)*cos(54�) - sin(90�)*sin(54�) =  = .

Solved. The answer is cos(144�) = .

RELATED QUESTIONS
1/t+3/t+5/t.....+t-1/t determine the number of terms in the series in terms of t (answered by greenestamps)

Write tan(t) in terms of csc(t) if t is in Quadrant... (answered by lwsshak3)

Express tan t in terms of cos t, if the terminal point determined by t is in quadrant II. (answered by Alan3354)

Express tan t in terms of sin t, if the terminal point determined by t is in Quadrant... (answered by Alan3354)

Use fundamental identities to write the first expression in terms of the second, if 0 < t (answered by ikleyn)

if 2t+(s-r)/3= t what is s in terms of r and... (answered by drj,Theo)

if {{{ t=x-1 }}} and {{{ y=t^2-3t+2 }}}, express y in terms of... (answered by Alan3354)

If the charge is $16 for t=0 minutes and c=$19.50 for 35 minutes, find the linear... (answered by lwsshak3)

The area of a rectangle with width t is given by 33t - t^2. Factor the expression and... (answered by edjones)