Use the diagram to complete the statements about how to prove the cosine sum identity. A unit circle. Point P is on the circle o
n the x-axis at (1, 0). Point S is in quadrant 4 on (cosine (negative beta), sine (negative beta) ). Point Q is in quadrant 1 above point P at (cosine (alpha), sine (alpha) ). Point R is above point Q at (cosine (alpha + beta), sine (alpha + beta) ). Triangles AOC and BOD are congruent by SAS. Therefore, and these lengths can be found using the . Because this is the unit circle, the coordinates of points A, B, and D are equal to cosine and sine of Alpha + Beta , Alpha, and –β, respectively. Write expressions for the lengths and set them equal. Rewrite cos(-Beta) and sin(-Beta) using the identities before squaring both sides of the equation. Simplifying the resulting expressions involving cosine and sine of Alpha, Beta, and Alpha + Beta requires using the identity. When simplified, the equation becomes cos(Alpha + Beta) = cos(Alpha)cos(Beta) - sin(Alpha)sin(Beta).
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we have
<u>The system of equations</u>
-------> equation
-------> equation
Substitute equation in equation
subtract both sides
Divide by both sides
the solution is the point
therefore
the answer is
the solution to the system of equations is the point