SOLUTION: y is directly proportional to x^2 and y=a for a particular value of x. Find an expression for y in terms of a, when this value of x is doubled. Please help me with this as fast

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Question 1078613: y is directly proportional to x^2 and y=a for a particular value of x. Find an expression for y in terms of a, when this value of x is doubled.
Please help me with this as fast as possible. I'm in hurry! Thank you.
Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
The phrase "y is directly proportional to x^2" means
y=k%2Ax%5E2 for a some constant k .
In that product, if you double x (you replace 2x for x ),
you get y=k%2A%282x%29%5E2=k%2A2%5E2%2Ax%5E2=k%2A4%2Ax%5E2=4%2A%28kx%5E2%29 ,
so you quadruple the value of y and get 4a .