Let the length and breadth of the rectangle be x cm and y cm repectively
So, as per the first condition
2(x+y)=20 -------------(1)
Again,
as per the second condition
x−y=4-------------(2)
Now,
solving equation (1),(2) by using determinant method
2(x+y)=20 -------------(1)
x+y=10
x−y=4-------------(2)
D=∣∣∣1−111∣∣∣=1×1−(−1)×1
=1+1
=2
Dx=∣∣∣4−1101∣∣∣=4×1−(−1)×10
=4+10
=14
Now,
Dy=∣∣∣14110∣∣∣=1×10−1×4
=10−4
=6
Again,
x=(Dx)D and y=(Dy)D
So, x=(14)2=7 and y=(6)2=3
Hence the length and breadth of the rectangle are 7cm and 3cm respectively.