Track / Stage 4 / 70 of 340 #330 of 2000

$$\text { 1. } a>0 \text {, and } \lg \left(49-a^{2}\right)-\lg \sqrt{a^{2}+49-14 a}=1$$

Then $a=$

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$-, 1.3$

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