If y varies directly with x², and y = 2 when x = 4, then y = 3 when x = 9.

Question

Find the error in the following computation. Then correct the error by rewriting the statement.

Answer 1

To vary directly means that one is a constant multiple of the other.

 

y = kx²

 

If y = 2 when x = 4, then 2 = k•4².

 

2 = 16k

1/8 = k

 

Therefore,

 

when y = 3,

 

3 = (1/8)x²

24 = x²

√24 = x

 

This is only one possible correction.  You could also have corrected y for when x = 9.