Question 1159265
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You are correct. You'll use the law of cosines to find the largest angle.


The largest angle is always opposite the longest side of any triangle. The largest side is 36 inches
a = 18
b = 25
c = 36


Let angles A,B,C be opposite sides a,b,c in that exact order. We want to find angle C as its opposite the longest side c = 36


Law of cosines
c^2 = a^2 + b^2 - 2*a*b*cos(C)
(36)^2 = (18)^2 + (25)^2 - 2*(18)*(25)*cos(C)
1296 = 324 + 625 - 900*cos(C)
1296 = 949 - 900*cos(C)
1296 - 949 = 949 - 900*cos(C)-949
347  = -900*cos(C)
(347)/(-900)  = (-900*cos(C))/(-900)
-0.385555555555556 = cos(C)
cos(C) = -0.385555555555556
arccos(cos(C)) = arccos(-0.385555555555556)
C = 112.678234158676
C = 113  after rounding to the nearest whole number



<font color=red size=4>Answer: A. 113 degrees (approximately)</font>
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