evaluate the given third-order determinants?

Question

-7 0 0
2 4 5
1 4 2

Answer 1

D=-7(4*2-4*5)-2(0-0)+1(0-0)
=7*(8-20)
=-84
ignoring thesign the value is 84

Answer 2

evaluate the given third-order determinants
-7 0 0
2 4 5
1 4 2


a1b1c1
a2b2c2
a3b3c3

where
a1 = -7
a2 = 0
a3 = 0

b1 = 2
b2 = 4
b3 = 5

c1 = 1
c2 = 4
c3 = 2

There is a formula on this site Please look at it so you will understand.

http://wps.prenhall.com/esm_blitzer_coll_alg_3/0,7207,700284-,00.html

look at Section 6.5 # 3

After you use the formula you will cross multiply and subtract to get the answer like this.

Note if you can't see everything
Put your mouse pointer on the ... to see the whole set of numbers.

a1(b2*c3-b3*c2)-a2(b1*c3-b3*c1)+a3(b1*c2-b2*c1)

-7(b2*c3-b3*c2)-2(b1*c3-b3*c1)+1(b1*c2-b2*c1)


-7(4*2-4*5)-2(0*2-4*0)+1(0*5-4*0) =

-7(8-20)-2(0-0)+1(0-0) =

-7(-12)-0+0 =

84

I hope this helps.
also look at
http://www.answers.com/topic/determinant

Answer 3

=7(4*2-4*5)
=84