Graphically find xx for which sinx=cosxsinx=cosx?

1 Answer
Sep 18, 2016

Please see below.

Explanation:

As sin(x+pi/2)=cosxsin(x+π2)=cosx, sinxsinx function moves with a gap of pi/2π2 with respect to cosxcosx. Between x=0x=0 and x=pi/2x=π2, cosxcosx falls from 11 to 00and sinxsinx rises from 00 to 11.

Further cos(-x)=cosxcos(x)=cosx and hence while cosxcosx is symmetric around yy-axis i.e. x=0x=0, As sinxsinx appears with a lag of pi/2π2, it is symmetric around x=pi/2x=π2.

Hence, cosx=sinxcosx=sinx appears exactly at the midpoint between 00 and pi/2π2 i.e. at pi/4=0.7854π4=0.7854
graph{(y-sinx)(y-cosx)=0 [-1.365, 3.635, -1, 1.5]}