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trig

posted by on .

What is the angle B?

Given that
A=46 degree
b=4
c=8

  • trig - ,

    Is this a triangle?

    Law of Cosines:

    a^2=b^2+c^2-2bcCosA
    solve for a.
    Then, law of sines:

    sin46/a=sinB/b
    solve for sinB, then B

  • trig - ,

    LAW OF COSINES: CosA=(b^2+c^2-a^2)/2bc

    Cos46=(16+64-a^2)/2*4*8.
    Cos46=(80-a^2)/64, 80-a^2=64Cos46,
    a^2=80-64Cos46=35.54, a=5.96=6.0

    LAW of SINES: SinB/b=SinA/a

    SinB/4=Sin46/6,Multiply both sides by 4: SinB=4*Sin46/6=0.4791, B=28.66=28.7

  • trig - ,

    and easy way to check this is to grab your protractor and sketch it to see if it works.

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