Find a unit vector with a negative i component that is orthogonal to both i + j and i + k.?

(Express your answers in terms of i for i, j for j and k for k.)

I got (1/(3^(1/2))i - (1/(3^(1/2))j -(1/(3^(1/2))k BUT the site says it's wrong. I'm unsure how to proceed
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