Please let me know the mistake in this equation:
-20=-20
16-36=25-45
42 -4*9=52-5*9
42 - 2*4* 9/2=52 -2*5* 9/2
(4-9/2)2 = (5-9/2)2
4=5
Simplify the following:3n×9n+13n−1×9n−1