Hello!
So you will use the Pythagorean Theron equation which is Asquare + bsquare=C square
Plug in what you are given to find the missing piece
A square+ (2.6)square= (6.2) square
Asquare+ 6.76= 38.44
(Subtract 6.76to both sides to isolate A)
Asquare= 31.68
(Take the square root of both sides to find out what A is)
A=5.628
