Specific Question About Solving: In a TV, the screen height is 0.75 times the screen width. It measures 39 inches diagonally, what is the screen width?

Question

I’ve seen the solution to this problem, but am confused as to why a certain step is taken.

w^2+0.75w^2=1521 becomes

w^2+0.5625w^2=1521

Why/How does 0.75w^2 become 0.5625w^2 in solving this problem?

Thanks in advance.

Answer 1

0.75² = 0.5625

Parentheses should be about 0.75w.