The value of cos (2 cos–1x + sin–1x) at x = 15 is

cos (2 cos–1x + sin–1x)= cos (cos–1x + cos–1x + sin–1x)=cos⁡π2+cos−1⁡x=−sin⁡cos−1⁡x=−sin⁡sin−1⁡1−x2=−1−x2=−1−125=−265