Question

-15x + x²/3=x²+5. (x²-3x)

Answer 1

-45x + x²= 3.x²+15.(x²-3x)
-45x + x² = 18x²-45x
x² = 18x²
17x² = 0
x' = 0
x'' = 0

r==0

Answer 2

-15x +15x +x²/3 -x² -5x² = 0
+x²/3 -x²= 6
+x² +x²= 6.3
2x²= 18
x²= 18/2
x²= 9
x=3