Question

Find the values of following determinants.
| -1 7|
| 2 4|

Answer 1

if any determinant A is written as
$A = \left|\begin{array}{cc}a&b\\c&d\end{array}\right|$
then, modulus of A or, value of A is given by
multiply of a and d - multiply of b and d
e.g., |A| = ad - bc
use this concept here,

Given,
$A= \left|\begin{array}{cc}-1&7\\2&4\end{array}\right|$
|A| = (-1) × 4 - 7 × 2 = -4 - 14 = -18
hence,value of determinant = -18

Answer 2

DETERMINANT :
|a b |
|c d |
is a determinant. (a, b), (c, d) are rows and , | a| ,|b |
                                                                        |c | , |d |are columns.
There are 2 elements in each column and 2 elements in each row so the Degree of this determinant is 2. It represents a number which is (ad-bc). ad-bc is the value of determinant |a b |
                     |c d |

SOLUTION :
GIVEN :
D = | -1  7|
       | 2   4|

D = |a b |
       |c d |
Determinant (D) = ad-bc

a= -1, b= 7 , c= 2 , d= 4 

D = (-1 × 4 ) - (7 × 2)
D = - 4 - 14 = -18
D = -18

Hence, the value of Determinant (D) is -18.

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