Question

Please answer the question

Answer 1

The angles of a triangle sum up to
`180^\circ`. So, if you know two of them (let's say
`\alpha` and
`\beta`), you can find the third angle
`\gamma` by subtraction:

`\alpha +\beta +\gamma = 180^\circ \iff \gamma = 180^\circ-\alpha -\beta = 180^\circ-(\alpha +\beta)`

So, in the first case, the given angles sum to
`120^\circ`, so the remaining one must be
`60^\circ`

In the second case, the given angles sum to
`19^\circ`, so the remaining one must be
`161^\circ`

In the third case, the given angles sum to
`108^\circ`, so the remaining one must be
`72^\circ`

In the fourth case, the given angles sum to
`159^\circ`, so the remaining one must be
`21^\circ`

Finally, the triangle with two sides of the same length is the one with two angles of the same measure, so the third one, which is isosceles.

Answer 2

I believe it is number iii #3