SOLUTION: A Triangle has sides of 21cm, 17cm and 10cm. Find the smallest angle

Question 251669: A Triangle has sides of 21cm, 17cm and 10cm. Find the smallest angle
Answer by checkley77(12844) (Show Source): You can put this solution on YOUR website!
USING THE LAW OF COS, WHEN 3 SIDES OF A TRIANGLE ARE KNOWN, WE GET:
COS 10=(17^2+21^2-10^2)/(2*17*21)
COS 10=(289+441-100)/714
COS 10=630/714=
C0S 10=.8824=28.07 DEGREES. THE SMALLEST ANGLE.
COS 17=(10^2+21^2-17^2)/(2*10*21)
COS 17=(100+441-289)/420
COS 17=252/420
COS 17=.6=53.13 DEGREES.
COS 21=(10^2+17^2-21^2)/2^10*17
COS 21=(100+289-441)/340
COS 21=-52/340
COS 21=-.153=98.8 DEGREES
PROOF:
28.07+53.13+98.8=180
180=180
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