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Trigonometry Question Help

Hello. I am stuck on this trig question.
The triangle ABC, shown in the diagram, is such that AB=5cm, AC=8cm,BC=10cm and angle BAC=Theta.
Show that Theta=97.9, correct to the nearest 0.1 degrees.
Any help would be appreciated
Original post by WhiteTigerKURD
Hello. I am stuck on this trig question.
The triangle ABC, shown in the diagram, is such that AB=5cm, AC=8cm,BC=10cm and angle BAC=Theta.
Show that Theta=97.9, correct to the nearest 0.1 degrees.
Any help would be appreciated


Remember this formula or did you forget?

Cosθ=b2+c2a22bc Cos \theta = \frac{b^2 + c^2 - a^2}{2bc}
Original post by LelouchViRuge
Remember this formula or did you forget?

Cosθ=b2+c2a22bc Cos \theta = \frac{b^2 + c^2 - a^2}{2bc}

Oh, I forgot about that. Thank you✌️✌
Original post by WhiteTigerKURD
Oh, I forgot about that. Thank you✌️✌


Are you doing Edexcel?

If so, you'll be given this in the formula booklet: a2=b2+c22bcCosA a^2 = b^2 + c^2 - 2bcCosA

This can just be rearranged for CosA Cos A

2bcCosA+a2=b2+c2 2bcCosA + a^2 = b^2 + c^2

2bcCosA=b2+c2a2 2bcCosA = b^2 + c^2 - a^2

CosA=b2+c2a22bc Cos A = \frac{b^2 + c^2 - a^2}{2bc}

Remember this bra ^^

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