Solution:
The equation below is given as
[tex]a^2=(c-x)^2+h^2[/tex]This represents the
PYTHAGOREAN THEOREM
The second equation is given below as
[tex]b^2=x^2+h^2[/tex]This represents the
PYTHAGOREAN THEOREM
The third expression is given below as
[tex]\cos A=\frac{x}{b}[/tex]This represents
Definition of cosine
The fourth expression is given below as
[tex]a^2=c^2-2c(bcosA)+b^2[/tex]This represents
Substitution property of equality