Hello, Ideasman!

If no one is responding, it's that the problem makes no sense.

. . I did an autopsy and came up with a COD . . .

int[sqrt(2/L)*sin((n*Pi*x)/L)]dL .??

The hint given is to use the trig identity:

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Could this be the problem?

. .

. . . . . . . . . . . . . . . . .

Apply the identity:

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The problem becomes:

. .

Then use substitution: . and