Find the range of max values of x

[ridhamshah]

x^4 + y^4=100

What is the range of values of x?

a) 0 to 3
b) 3 to 6
c) 9 to 12
d) 12 to 15

To solve it for max value of x, i put y^4 to 0 and solved for x^2 = 100 or x to be max of 3.
So my choice was a) but seems like the solution was b).

any ideas on how to solve this?

[Ben Ku]

Please cite the source (author) of this problem. We cannot reply unless a source is cited (and, if no source is cited, we will have to delete the post!). Thanks.