Angles by cosine law

Calculate the size of the angles of the triangle ABC if it is given by: a = 3 cm; b = 5 cm; c = 7 cm (use the sine and cosine theorem).

Correct answer:

α =  21.7868 °
β =  38.2132 °
γ =  120 °

Step-by-step explanation:

a=3 b=5 c=7  a2 = b2+c2  2 bc cos α A=arccos((b2+c2a2)/(2 b c))=arccos((52+7232)/(2 5 7))0.3803 rad  α=A  °=A π180   °=0.3803 π180   °=21.787  °=21.7868=21°4712"
b2 = a2+c2  2 ac cos β B=arccos((a2+c2b2)/(2 a c))=arccos((32+7252)/(2 3 7))0.6669 rad β=B  °=B π180   °=0.6669 π180   °=38.213  °=38.2132=38°1248"

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