Why does this API call result in a computation error?

Questions
1

Hi,
I’m new to Wolfram Alpha, just trying to use it to solve some equations and get the results back into a Google Sheets document. Here’s an example of what I’m trying to get it to solve.

Works fine, right? Similarly, if I put that query into the API explorer, it gives me a query URL with an input portion that matches the URL in my original test:

http://api.wolframalpha.com/v2/query?appid=xxx&input=(0.05660377358490565^-a%20%3D5.263157894736842*0.4339622641509434^-a%20%2B%201%20-%205.263157894736842)&format=plaintext

But if I put my App ID into that URL, rather than getting the answer back, I get a mysterious error message:

<queryresult success="false" error="true" numpods="0" datatypes="" timedout="" timedoutpods="" timing="1.879" parsetiming="0." parsetimedout="false" recalculate="" id="" host="http://www4b.wolframalpha.com" server="38" related="" version="2.6">
<error>
<code>1010</code>
<msg>Computation error</msg>
</error>
</queryresult>

Why is that happening? It works everywhere except in the one place I actually need it to work!