SOLUTION: Solve: cos(x) cos (6x) =-1

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Question 1159951: Solve: cos(x) cos (6x) =-1
Found 2 solutions by MathLover1, ikleyn:
Answer by MathLover1(20850)   (Show Source): You can put this solution on YOUR website!


-> you know that

case 1: when and




and
general solutions for is:




check: if
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case 2: when and








check: if
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Answer by ikleyn(52786)   (Show Source): You can put this solution on YOUR website!
.

HINT.  This equation can be satisfied IF and ONLY IF  one of the two factors in left side is equal to -1, 
while the other factor is equal to 1.


Answer.   x =  = 180°.


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