Use Subtraction
1. Subtract
x+2y=7
3x-2y=-3
-------------
4x+0y=4 SIMPLIFY 4x=4
2. DIVIDE
4x=4
x=1
Substitute that into either of the original equations to get x=1, y=3
it equals <span>(−<span>12</span>)</span> because <span><span>cos<span>(<span>60∘</span>)</span></span>=<span>12</span></span>
Explanation:
The reference angle for <span>240∘</span> is <span>60∘</span> (since <span><span>240∘</span>=<span>180∘</span>+<span>60∘</span></span>)
<span>60∘</span> is an angle of one of the standard triangles with
<span><span>cos<span>(<span>60∘</span>)</span></span>=<span>12</span></span>
<span>240∘</span> is in the 3rd quadrant so (either by CAST or noting that the "x-side" of the associate triangle is negative)
<span><span>cos<span>(<span>240∘</span>)</span></span>=−<span>cos<span>(<span>60∘</span>)</span></span></span>
<span><span>cos<span>(<span>240∘</span>)</span></span>=−<span><span>12</span></span></span>
The answer is 4900 because you add the 6,400+1,800=8,200 then you subtract the 8,200-3,300= 4,900
