How do I verify this equation is an identity? cos(x+y)/cosx cosy=1-tanx tany
1 Answer
Mar 18, 2018
Explanation:
#"using the "color(blue)"trigonometric identity"#
#•color(white)(x)cos(x+y)=cosxcosy-sinxsiny#
#"consider the left side"#
#(cos(x+y))/(cosxcosy)#
#=(cosxcosy-sinxsiny)/(cosxcosy)#
#=cancel(cosxcosy)/cancel(cosxcosy)-(sinxsiny)/(cosxcosy)#
#=1-(sinx/cosx xxsiny/cosy)#
#=1-tanxtany=" right side "rArr"verified"#