What is the length of a if a triangle has lengths of b=6.4cm and c=5.6cm with an angle A=107.9 degrees?

We are going to have to use the cosine rule for this type of question. The cosine rule is a2=b2+c2 - 2bcCosATherefore a2= (6.46.4) + (5.65.6) - (26.45.6)*Cos107.9 If we plug this into our calculator we will get a2= 94.3513...Then we square root a2 to get 9.7cm (1.d.p) - because all other values in the question are rounded up to 1 decimal place.