how do I solve for a

Answer:
using the pythagoras theorem the answer is a=3
Step-by-step explanation:
basically in a right angled triangle a² + b² equals c². in this equation c is the number on the hypotenuse (the line opposite the right angle)
and 4 could be a or b it doesnt make a difference so I'll call it b.
because we have c² and b² we work backwards like this:
[tex] {5}^{2} - {4}^{2} = {a}^{2} [/tex]
[tex] {5}^{2} - {4}^{2} = 25 - 16 = 9[/tex]
because 9 is a², we must find the square root to find a
[tex] \sqrt{9 } = 3[/tex]
so a equals 3