Question

Which sum or difference identity could be used to prove that cos(270°-theta)=-sin theta is an identity?

Answer 1

For this case we have that by definition:

$cosine (a-b) = Cosine (a) * cosine (b) + sine (a) * sine (b)$

If we want to solve $cosine (270-theta)$then:

$cosine (270-theta) =\\cosine (270) * cosine (theta) + sine (270) * sine (theta) =$

We know that:

$cosine (270) = 0\\sine (270) = - 1$

Substituting:

$cosine (270) * cosine (theta) + sine (270) * sine (theta) =\\0 + (- 1 * sine (theta)) =\\-sine (theta)$

Answer:

$cosine (a-b) = Cosine (a) * cosine (b) + sine (a) * sine (b)$

Answer 2

Answer:

Your answer would be B.

Step-by-step explanation: