Q)A rectangular field , 70m long and 50m wide, has a path of uniform width around it .If the area of the path is 1024m^2 , find the width of the path.

Solutionlet x be the uniform width of the path

According to the given condition,

(50+2x)(70+2x)-1024=50*70

...............................

and the answer comes out to be 4m after solving this.

I have problem in that how the bold equation is formed ?