Help plzzz:

In a triangle PQR, 2 of the sides are 5 units long and the included angle is 100°. How long is the third side?

Question

Help plzzz:

In a triangle PQR, 2 of the sides are 5 units long and the included angle is 100°. How long is the third side?

anonymous · Answer

|dw:1408536707289:dw|

anonymous · Answer

you know cosine formula??

anonymous · Answer

yea i do but i dont understand it very well

anonymous · Answer

see it's like,
$$a^ 2 = b ^2 + c ^2 − 2bc \cos A$$
where both sides b and c has been given and angle A is also given, just need to substitute in it

anonymous · Answer

okayy ill try it out

anonymous · Answer

yeah!! go on )

anonymous · Answer

So is this right?$$5^2 = 5^2 + c^2 - 2 * 5c * Cos(100)$$

anonymous · Answer

when substituted?

anonymous · Answer

oh!!! no actually from my equation you need to calculate "a"...your b and c are the terms are given )

anonymous · Answer

oh yea course so $$a^2 = 5^2+5^2-2*5*5*\cos(100)$$

anonymous · Answer

yeah that one @FishFingersandCustard  Now calculate a from that equation )

anonymous · Answer

thanks so much @aryandecoolest helped so much :D

anonymous · Answer

no problem ) pleasure to help :D @FishFingersandCustard