# Thread: Question about simple multiplication

1. ## Question about simple multiplication

Sorry about all my threads, but hope you guys can help me once again.
Just a simple question.

f(x) = a + bcos2x
f(0) = a + bcos2(0) = -1

Now this is where I'm slightly confused. "Anything multiplied by 0 is 0", right, and because b is multiplied to cos2(0), then surely that removes b and you get:

f(0) = a + b(0)
f(0) = a = -1

But, according to the textbook, it's not. They say its:

f(0) = a + b = -1

Why?

2. ## Re: Question about simple multiplication

Originally Posted by yorkey
Sorry about all my threads, but hope you guys can help me once again.
Just a simple question.

f(x) = a + bcos2x
f(0) = a + bcos2(0) = -1

Now this is where I'm slightly confused. "Anything multiplied by 0 is 0", right, and because b is multiplied to cos2(0), then surely that removes b and you get:

f(0) = a + b(0)
f(0) = a = -1

But, according to the textbook, it's not. They say its:

f(0) = a + b = -1

Why?
cos(2x0) = cos(0) = 1.

3. ## Re: Question about simple multiplication

Originally Posted by yorkey
Now this is where I'm slightly confused. "Anything multiplied by 0 is 0", right, and because b is multiplied to cos2(0)
But $\displaystyle \cos(2\cdot0)=\cos(0)=1$, not 0. I am sure you don't think that $\displaystyle \cos(0) = {\cos}\cdot0=0$.

4. ## Re: Question about simple multiplication

Oh. Actually I did think that cos(0) = 0. I... didn't think.

Sorry for the trouble! Thanks again.