Can some explaine the Q27 from GRE9367?

I select B, but the correct answer is A.

I do not know why f(y) should be f(y)^2.

sorry, I can not write the Q here, because I do not have Latex:(

Thanks

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about Q 37 also I have problem,

I chose A as answer, because the first row product in 3 , then det =9*3=27 and after that the third row product in -4, then det=27*(-4)=-108,

but answer is -27. I do not know why:( can someone explain that?

Thanks

## GRE9367#27and 37

### Re: GRE9367#27and 37

#27

x^2 + z^2 = r^2 in the plane y = y_0, and f(y_0) is the radius.

#37

You are exchanging rows 2 and 3, which gives you a negative 27

Now, to the new row 2 you are adding the new row 3 times a constant. This doesn't change the determinant. If you dont see why, calculate this

|a b|

|c d|

And the same while adding to any line the other one times any number you choose

x^2 + z^2 = r^2 in the plane y = y_0, and f(y_0) is the radius.

#37

You are exchanging rows 2 and 3, which gives you a negative 27

Now, to the new row 2 you are adding the new row 3 times a constant. This doesn't change the determinant. If you dont see why, calculate this

|a b|

|c d|

And the same while adding to any line the other one times any number you choose