The third one :) I hope I did it right
Unsure what you mean by diagonal right triangle
but if you wanted to find the hypothenuse (longest side) of a right triangle, you can apply pythagorean theorem

where c is the hypothenuse
a and b are the other sides
Draw a number line with 10 positives and 10 negatives. Count from 0 to 8. Now, from 8, count back 12 spots. From that spot, go back to 0, which is their original position. The number you counted there is your answer.
For this case we have the following function:

We change the variables:

From here, we clear the value of y.

Then, we make the following change:

Finally, the inverse function is:

Answer:
The inverse of the given relation is:

Answer:

Step-by-step explanation:
Based on the given conditions, formulate: 
Convert decimal to fraction:
Divide a fraction by multiplying its reciprocal:
Cross out the common factor: 
Calculate the product or quotient: 
get the result: 
Answer: 