Friday, July 30, 2010

`A = 120^@, b = 6, c = 7` Use the Law of Cosines to solve the triangle. Round your answers to two decimal places.

The given in the triangle are `A=120^o` , `b=6` and `c=7` . To solve for the values of a, B and C, let's apply Cosine Law.


For side a:


`a^2=b^2+c^2-2*b*c*cosA`


`a^2=6^2+7^2-2*6*7cos(120^o)`


`a^2=36+49-84cos(120^o)`


`a^2=127`


`a=sqrt127`


`a=11.27`


For angle B:


`b^2=a^2+c^2-2*a*c*cosB`


`6^2=(sqrt127)^2+7^2-2*sqrt127*7*cosB`


`36=176-14sqrt127cosB`


`(36-176)/(-14sqrt127)=cosB`


`cos^(-1)((36-176)/(-14sqrt127))=B`


`27.46^o=B`


For angle C:


`c^2=a^2+b^2-2*a*b*cosC`


`7^2=(sqrt127)^2+6^2-2*sqrt127*6*cosC`


`49=127+36-12sqrt127cosC`


`49=163-12sqrt127cosC`


`(49-163)/(-12sqrt127)=cosC`


`cos^(-1)((49-163)/(-12sqrt127)=C`


`32.54^o=C`


Thus, the sides of the triangles are:


`a=11.27`


`b=6`


`c=7`


And its angles are:


`A=120^o`


`B=27.46^o`


`C=32.54^o`

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