Try to explain (a + 3) &# 178; ≠ A & # 178; + 3 & # 178; (a ≠ 0) in a direct way

Try to explain (a + 3) &# 178; ≠ A & # 178; + 3 & # 178; (a ≠ 0) in a direct way

As shown in the picture
If the outside is a square a + 3 longer than the side, then its area is (a + 3) &;
Divide its side into two parts A and 3, and make two small squares to the inside of the square respectively
Then, their areas are a & # 178;, 3 & # 178;
Obviously, the area of a large square is not equal to the sum of the areas of two small squares
That is, (a + 3) &# 178; ≠ A & # 178; + 3 & # 178; (a ≠ 0)

What is 300 & # 178; + (400-x) &# 178; equal to?

300²+(400-x)²
=90000+x²-800x+160000
=x²-800x+250000

R & # 178; = 300 & # 178; + (r-90) &# 178; how to solve this equation? Is it a quadratic equation with one variable? Please write down the process. Thank you

You can understand r as X, that is
Do not write down this step
X²=90000+X²-180X＋8100
180X=98100
X=545
Namely
R²=90000+R²-180X＋8100
180R=98100
R=545