If 1 + cosxcosx - 2sin^2xsin2x = 0 , what is the value of xx? Precalculus Graphs of Trigonometric Functions Graphing Sine and Cosine 1 Answer Cesareo R. Jun 11, 2016 x = { pm pi +2k pi} uu {pm pi/3 + 2k pi} x={±π+2kπ}∪{±π3+2kπ} for k = 0,pm1,pm2,pm3,... Explanation: Making sin(x)^2=1-cos(x)^2 and y = cos(x) we obtain 1+y-2(1-y^2)=0 Solving for y we have {y=-1,y=1/2} so the solutions for x must obey cos(x) = -1 or cos(x) = 1/2 Solving for x we obtain x = pm pi +2k pi for cos(x) = -1 and x = pm pi/3 + 2k pi for cos(x) = 1/2 for k = 0,pm1,pm2,pm3,... Answer link Related questions What is the y-intercept of the graph of y = sin x? What is the graph of y=sin (x/3)? What is the graph of y=sin(x+30)? What is the graph of y=sin(x-pi/4)? What is the graph of y=sin(x/2)? What is the amplitude of the graph of y = sin x? What is the range of the graph of y = sin x? What are the x-intercepts of the graph of y = cos x? What is the domain of the graph of y = cos x? What is the maximum value that the graph of y=cos x assumes? See all questions in Graphing Sine and Cosine Impact of this question 2516 views around the world You can reuse this answer Creative Commons License