SOLUTION: A cosine graph goes through the points (0,a) and (3π/4, -a). If the equation of the graph is {{{y=acoskx}}}, and {{{k=1}}}, what is the value of {{{a}}}?

Algebra ->  Trigonometry-basics -> SOLUTION: A cosine graph goes through the points (0,a) and (3π/4, -a). If the equation of the graph is {{{y=acoskx}}}, and {{{k=1}}}, what is the value of {{{a}}}?      Log On


   

Question 1118125: A cosine graph goes through the points (0,a) and (3π/4, -a). If the equation of the graph is y=acoskx, and k=1, what is the value of a?
Answer by math_helper(2461) About Me  (Show Source):
You can put this solution on YOUR website!
+highlight%28a=0%29 (or else there is an error in the problem statement).

k=1 so we can write cos%28k%2Ax%29+=+cos%28x%29+

Consider +x=+3%28pi%29%2F4+ :

+cos%283%28pi%29%2F4%29+=+-sqrt%282%29%2F2+ or about -0.7071, so a*cos(x) is -0.7071*a there. Yet, the problem statement says it should be -a. The function can not be both -a and -0.7071a for any nonzero value of a.