Question

For orthogonal and nonorthogonal contrasts: What is the covariance equal to between their corresponding predictors?

What is the correlation equal to between these predictors?

Answer 1

orthogonal and uncorrelatedness is the same thing .

if there is no correlation between the two given predictors then the condition of orthogonality originates .

and if there is no correlation between the predictors means covariance term is zero

so for orthogonality  the covariance equal to between their corresponding predictors

and  the correlation equal to between these predictors is also zero

but in case of  nonorthogonal contrasts the given condition for orthogonality becomes vice versa.