PLEASE HELP.Consider ABC with the measure of angle B equal to 60 degrees, and side lengths a=4 and c=5. Which option lists an expression that is equivalent to the length of side b?
Accepted Solution
A:
we know that the law of cosines establish b²=a²+c²-2*a*c*cos B in this problem a=4 units c=5 units B=60° so b²=a²+c²-2*a*c*cos B b²=4²+5²-2*4*5*cos 60° b²=16+25-40*(1/2) b²=16+25-20 b=√[16+25-20]