Triangle Units

Hello,
I hope you can help me solve this question.

A triangle has sides of length 4, 5, 7 units. Find, to the nearest tenth of a degree, the size of the largest angle.

Thanks.

Hi
You can use the cosines formula
a,b,c being the lengths of the sides of a triangle
A,B,C being the angles (A is the angle formed with sides whose length are b anc c (opposite to the length a))
a²=b²+c²-2bc cosA
Then cosA=(b²+c²-a²)/(2bc)

Thanks :)