Question 984965
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1.Indicated sum:
c=-3 (coefficient of k), n=15, x=constant=2
(1/2)cn(n+1)+2(x)
(1/2)(-3)(15)(16)+2(15)
-360+30=-330 ANSWER: -330
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2. Standard position starts on x-axis pointing positive from origin turning counterclockwise. 
The negative angle would turn clockwise so the answer is the third, 236991.jpg
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3. Law of Cosines:
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{{{cosA=(b^2+c^2-a^2)/2bc}}}
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{{{A=arccos((b^2+c^2-a^2)/2bc)}}}
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{{{cosB=(c^2+a^2-b^2)/2ca}}}
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{{{B=arccos((c^2+a^2-b^2)/2ca)}}}
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A+B+C=180 degrees
C=180-A-B
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Just fill in values: a=15; b=11; c=7
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{{{A=arccos((11^2+7^2-15^2)/2(11)(7))}}}
{{{A=arccos(-55/154)}}}
{{{A=arccos(-0.3571)}}}
{{{A=110.9degrees}}}
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Try the rest on your own. Equations given above.
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