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4.

(i)

By Pythagoras’ Theorem,

(ii)

Perimeter

When

When $latex x = 8, y = 6 < x$, which is not possible given the question. Thus, rejected. $latex \therefore, x=4, y=18$

### KS Comments

Students need to be alert to reject the appropriate x-value. Alternatively, they can also check the second order derivative to determine which is the suitable x value.

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