Show that cos(a+45)=cos45(cosa-sina)

Hello here is a solution :
co(a+b)  =cosacosb -sina sinb
cos(A+45)=cosAcos45-sinAsin45
cos45=sin45

cos(A+45)=cosAcos45-sinAcos45=cos45(cosA-sinA)

I’m pretty sure the * means multiplication. so, if you multiply 5*1, it would equal 5. they are basically are-writing 5x1 as 5*1. so they would be… 5 10152025303540455055