UPSC NDA I 2021 Mathematics Solved Paper

Concept:
Suppose A is a square matrix of 2 rows and 2 columns
A=[

a	b
c	d

]
The determinant is; |A|=[ad−bc]
Calculation:
A=|

p	q
r	s

|
p,q,r and s are any four different prime numbers less than 20 .
Here we have to find the maximum value of the determinant so we have to take maximum value for p and
All prime numbers less than 20=2,3,5,7,11,13,17,19
So, p=17,q=2,r=3 and s=19
A=|

17	2
3	19

|
|A|=[17×19−2×3]
‌‌=323−6
‌‌=317