Question

Using E= mc2 , solve for m. Then, find the value of m if E = 725 and c= -5

Answer 1

Divide by c^2, m=E/(c^2)
M=725/(-5)^2
M=725/25
M=29

Answer 2

$E=mc^2\ \ \ \ |:c^2\\\\m=\frac{E}{c^2}\\\\m=\frac{725}{(-5)^2}\\\\m=\frac{725}{25}\\\\\boxed{m=29}$