Let f(x)=cos[π2]x+cos[−π2]x,where [ .] represents greatest integer function,then f(π2)=−1 and f(−π)=?
Weknowthat,π=3.14Then,(π)(π)∼9somethingi.e9<π2<10Now,f(x)=cos(9x)+cos(−10x),orf(x)=cos(9x)+cos(10x)[As.cos(−x)=cosx]Now,f(π2)=cos(9π2)+cos(10π2)=cos(9π2)+cos(5π2)=cos(4π+π2)+cos(4π+π)=cos(π2)+cos(π)=0−1=−1Similarly,f(−π)=cos(−9π)+cos(−10π)=cos(9π)+cos(10π)=cos(8π+π)+cos(10π)=cos(π)+cos(0)=−1+1=0