The the slope of his indifference curve at the point (8; 9) is -05.
It should be noted that the slope of an indifference curve is the change in Y over the change in X.
The utility will be:
U = min(6 × 8, 8 + 2 × 9)
U = min(57, 26).
The change in utility will be:
= ∆y/∆x = (9 - 9.5)/(8 - 7)
= -0.5/1
= -0.5
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