Dilations of graphs issue....

[turtle turtle]

Question: There's a point (3, 9) that undergoes "a horizontal stretch with scale factor 1/2"

The answer for the new point is (3/2,  9).

But since it's a dilation in the y axis, should it be multiplied by 2, not half ?

[kw0573]

This is purely a concern about word choice. "Stretch" can be interpreted as both stretch and compression. Typically for the factors less than 1, the word "compression" is used, but "stretch" is equally valid. It's like saying a temperature rise of -4°C means a decrease of +4°C but you know what they are talking about. IB would not use the word "factor" to denote a coefficient in the function. If (3,9) was part of a function then you would be given f(x) and asked to find f(2x). "2" would never be called a factor by IB. 

[turtle turtle]

5 hours ago, kw0573 said:

This is purely a concern about word choice. "Stretch" can be interpreted as both stretch and compression. Typically for the factors less than 1, the word "compression" is used, but "stretch" is equally valid. It's like saying a temperature rise of -4°C means a decrease of +4°C but you know what they are talking about. IB would not use the word "factor" to denote a coefficient in the function. If (3,9) was part of a function then you would be given f(x) and asked to find f(2x). "2" would never be called a factor by IB. 

Thanks for the reply, but the IB question said there's a stretch of factor 1/2, and i was confused because i thought that meant you multiply the point by 2 rather than 1/2