Track / Stage 4 / 73 of 340 #333 of 1964

(1) In an isosceles triangle with a perimeter of 30, the base length is $y$, and the leg length is $x$. The functional relationship between $y$ and $x$ is $y=$ $\qquad$ .

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Official solution

1) $30-2 x\left(\frac{15}{2}<x<15\right)$

Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic, difficulty and ordering added by this site.