Question

A triangle has sides A, B, and C. Sides A and B are of lengths `4` and `2`, respectively, and the angle between A and B is `(2pi)/3`. What is the length of side C?

Answer 1

`C=5.3`

Explanation:

As per law of cosines
`C^2=A^2+B^2-2Atimes Btimescos(theta)` where `A=4;B=2 and theta=(2pi)/3`
or
`C^2=4^2+2^2-2times4times2timescos((2pi)/3)`
or
`C^2=16+4-16times(-0.5)`
or
`C^2=20+8`
or
`C^2=28`
or
`C=sqrt28`
or
`C=5.3`