Laplace transform: steps between f(t)= cos(t-5+5)H(t-5) and f(t)= cos(t-5)cos5 H(t-5)

[Hannah]

I can't find the steps between
f(t)= cos(t-5+5)H(t-5)
and
f(t)= cos(t-5)cos5 H(t-5)-sin(t-5)sin5 H(t-5)

Thanks in advance

 

[Steven G]

I can't find the steps between
f(t)= cos(t-5+5)H(t-5)
and
f(t)= cos(t-5)cos5 H(t-5)-sin(t-5)sin5 H(t-5)

Thanks in advance

What is the expansion of cos(a-b)? This is an old trigonometry identity. If you still are having trouble, then write back with the formula for cos(a-b) and you will get help from there.

 

[Hannah]

What is the expansion of cos(a-b)? This is an old trigonometry identity. If you still are having trouble, then write back with the formula for cos(a-b) and you will get help from there.

I got it, thanks!