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(-1,-2) would result in a relation that is no longer a function.

In the table, there's already x = -1 and y = -4. Function only gives a single y-value with x-value. If a single x-value gives two y-values then it'd not be Function.

If we add (-1,-2) in the table. The domain will be repetitive. Basically, we already have (-1,-4) and if we add (-1,-2) in the table, a single x-value will give TWO y-values which is not a function.

the sum of all the angles in a triangle are equal to 180

so you can add   the 3 given angles together to equal 180:

5y + 2y + 2y = 180

or since all three angles have the same letter, combine the 3 angles to equal 180:

9y = 180