Answer:
The work is in the explanation.
Step-by-step explanation:
The sine addition identity is:
.
The sine difference identity is:
.
The cosine addition identity is:
.
The cosine difference identity is:
.
We need to find a way to put some or all of these together to get:
.
So I do notice on the right hand side the
and the
.
Let's start there then.
There is a plus sign in between them so let's add those together:

![=[\sin(a+b)]+[\sin(a-b)]](https://tex.z-dn.net/?f=%3D%5B%5Csin%28a%2Bb%29%5D%2B%5B%5Csin%28a-b%29%5D)
![=[\sin(a)\cos(b)+\cos(a)\sin(b)]+[\sin(a)\cos(b)-\cos(a)\sin(b)]](https://tex.z-dn.net/?f=%3D%5B%5Csin%28a%29%5Ccos%28b%29%2B%5Ccos%28a%29%5Csin%28b%29%5D%2B%5B%5Csin%28a%29%5Ccos%28b%29-%5Ccos%28a%29%5Csin%28b%29%5D)
There are two pairs of like terms. I will gather them together so you can see it more clearly:
![=[\sin(a)\cos(b)+\sin(a)\cos(b)]+[\cos(a)\sin(b)-\cos(a)\sin(b)]](https://tex.z-dn.net/?f=%3D%5B%5Csin%28a%29%5Ccos%28b%29%2B%5Csin%28a%29%5Ccos%28b%29%5D%2B%5B%5Ccos%28a%29%5Csin%28b%29-%5Ccos%28a%29%5Csin%28b%29%5D)


So this implies:

Divide both sides by 2:

By the symmetric property we can write:

Answer:
(-18,9)
Step-by-step explanation (work shown in picture attached):
1) The first step in solving by substitution is to isolate the y-term in one of the equations if it is not already isolated. Isolate y in the first equation by dividing both sides by -2. This leaves us with the equation
2) Now, substitute
for the y in the second equation. Simplify and isolate x. (You can multiply everything by -2 to get rid of the fraction.) This leaves us with x = -18.
3) We've found the x-value of the solution, -18. Now, substitute -18 for x back into one of the original equations (I chose the first one because it was simple) and isolate y. This gives us y = 9. Thus, in point form, the answer is (-18,9).
Answer:
Area: 135 ft^2
Perimeter: 50 ft
Step-by-step explanation:
area:
take the rectanle so length 12 x 9 = 108 so that is the length of the rectangle and now we need to find that of the triangle left over
subract 18 - 12 = 6 so that is the base of the trianle and we know the side length is 9 so plus it in A = (9)(6)/2
A = 54/2
A = 27
add 27 + 108 to get the total area
135
perimeter:
18 + 9 + 11 + 12 = 50