Denote each of the triangles ABC, where B is the right angle.
a.
[tex] t^{2}+ 12^{2}= 13^{2} [/tex]
instead of taking the square of 12 and 13, , take 12 squared to the right side and apply the difference of squares formula: [tex] a^{2}- b^{2}=(a-b)(a+b)[/tex]