Question #54875

1 Answer
CW
Jun 2, 2017

see explanation.

Explanation:

enter image source here

By the Law of Cosines, we know that:
c^2=a^2+b^2-2*a*b*cosangleC
Putting in the values, we get
9^2=4^2+7^2-2*4*7*cosangleC
=> cosangleC = (16+49-81)/(2*4*7)=-0.28571
=> angleC=cos^-1(-0.28571)=106.60^@

Similarly,
a^2=b^2+c^2-2*b*c*cosangleA
=> cosangleA=(9^2+7^2-4^2)/(2*9*7)=0.90476
=> angleA=cos^-1(0.90476)=25.21^@

=> angleB=180-angleC-angleA=180-106.60-25.21=48.19^@

Related questions
See all questions in Special Right Triangles
Impact of this question
2113 views around the world
You can reuse this answer
Creative Commons License