I think my math book is wrong...but I don't know. Could someone check and if it's not wrong, explain it to me?

Question

anonymous · Answer

here it is

nubeer · Answer

hmm what is your math book answer?

anonymous · Answer

That is the math book answer

nubeer · Answer

hmm and what is your answer?

anonymous · Answer

I know this can't be right but I got x=2.5. I don't understand how they randomly got the extra 2 when it should be a 9.

nubeer · Answer

ok.. i also have got a different answer but not sure.. so can you put steps how you solve it?

nubeer · Answer

and it's matrix right?

anonymous · Answer

it looks like its just a typing error, try asking or calling your teacher

raden · Answer

81x - 21x = 24
60x = 24
x = 24/60 = 2/5

anonymous · Answer

Yeah it's about evaluating determinants of a matrix.

How I solved the problem was:

(0)(1)(3)+(7)(2)(0)+(9)(x)(9)
(0)(1)(9)-(9)(2)(0)-(3)(x)(7)
0+0+81x-0-0-21x=24
60x=24
x=2.5

raden · Answer

2/5 = 4/10 = 0.4
not 2.5

phi · Answer

See http://www.wolframalpha.com/input/?i=det+%7B+%7B0%2C7%2C9%7D%2C%7B0.4%2C1%2C2%7D%2C%7B0%2C9%2C3%7D%7D x= 0.4 so there must be a typo somewheres?

phi · Answer

60x=24
x=2.5 ??   don't you think it is x= 24/60 = 2/5

phi · Answer

See http://www.wolframalpha.com/input/?i=det+%7B+%7B0%2C7%2C9%7D%2C%7B0.4%2C1%2C2%7D%2C%7B0%2C9%2C3%7D%7D x= 0.4 so there must be a typo somewheres?

phi · Answer

The book's solution would be correct if the first line of the matrix were
0 7 2   (rather than 0 7 9)