# If triangle abc is not right, how to determine a side if given 2 sides and angle?work ab=2,ac=4,angle a=60

### 1 Answer | Add Yours

Notice that the given angle `hatA` is an included angle, hence, you may use the law of cosines to find the missing length such that:

`(BC)^2 = (AB)^2 + (AC)^2 - 2AB*AC*cos 60^o`

You need to substitute `2` for `AB,4` for `AC` and `(1/2)` for `cos 60^o` , such that:

`(BC)^2 = 2^2 + 4^2 - 2*2*4*(1/2)`

`(BC)^2 = 4 + 16 - 8 => (BC)^2 = 12 => BC = sqrt12 => BC = sqrt(2^2*3)`

`BC= 2sqrt 3`

**Hence, evaluating the missing length, using the law of cosines, yields `BC= 2sqrt 3` .**

**Sources:**